The scene as presented is historically implausible.

Although some have objected that the Romans would probably not have permitted a man the crowd acknowledged King to enter the city to cheering crowds, Price (2003, p 292) argues that what is really going on is a bit of Markan irony. The crowd is simply giving out the Hosanna! as part of the usual Passover wish that the Davidic messiah would come and restore the Davidic monarchy. And sure enough, in front of them, is the Davidic messiah -- but the crowd doesn't know. To them, Jesus is just one of tens of thousands of entrants to the city for the Passover festival, who happens like thousands of others, to be arriving on a donkey.

In Mark's scene, the "crowd" does not acknowledge that Jesus is the messiah, whereas in Luke, they clearly do. However, the vast distance being traversed here during Jesus entrance, as well as the presence of both straw and garments, may be signals that Mark did not frame it the way Price is arguing.

Note also that in Mark there is no crowd. v9 says "And those who went before and those who followed cried out..." implying that the speaking is done not by a crowd but most probably by disciples who have come into Jerusalem. with Jesus. No crowd is ever directly mentioned, just the "many" who spread their garments on the road or lined it with branches.

Regardless of how one reads the entry, the salient fact is that the Romans had a low tolerance for even the slightest whiff of sedition, and would have dealt with it ruthlessly. As Brent Kinman (1994) concedes while attempting to defend the historicity of the incident, even among scholars who accept the historicity of the story, the reality of Roman touchiness on the subject of sedition creates apprehension. Kinman goes on to argue that since Pilate's coming up to Jerusalem must have been an extravagant affair, Jesus' entry must have paled beside it. While this approach is the distilled essence of speculation, Kinman does bring up one common point, that the Gospel portrayals need not be read as having the crowd in its entirety acknowledge Jesus the savior. Against this is Gundry's observation of the sheer length of Jesus dramatic entrance, as well as the details of the crowd laying things at his feet the whole way.

In any case, as we have seen, this passage is created off of the Old Testament. At the level of the overall framework, beginning with the arrival in Jerusalem the parallels to the Elijah-Elisha Cycle become ever denser. Here the writer of Mark begans to rely more and more on that cycle for his plot structure and the details of his story (Brodie 2000, p92):  

The E-E Cycle also explains some of the stranger details of this passage.  

The writer of Mark has also modeled this on the sequence in Zechariah 14. Duff (1992), who connects the entrance into the city to Zech 14, summarizes that text below. Note how the sequence in this text resembles this section of the Gospel of Mark, with the entrance into Jerusalem from the Mount of Olives, down a processional highway, accompanied by his holy ones.

At the detail level, the passage is a creation off of the sequence in 1 Samuel 9 and 1 Sam 10:

The scene may also represent a common convention of Greek drama, the hyporcheme, as proposed by Bilezekian (1977):

Duff (1992) also points out that the procession surrounding the entrance of the warrior-king into the city was originally modeled on Greek epiphany processions, in which the deity enters the city. Frequently the entering King is either greeted as a god, or performs sacrifices that "function as an act of appropriation" (p60).

This pericope consists of two chiastic structures looking more or less like this:

The presence of the supernatural juxtaposed with OT creation at both the level of detail and of the plot structure, along with the presence of Mark literary creation (the doublet of v1-6), and the conventionality of the entry in Greco-Roman culture indicate that there is no support for historicity in this pericope.

This pericope's chiastic structure is impossible to clearly specify. The wrter's A brackets are typically geographical movements, and there is nowhere else in the gospel where Jesus makes so many movements in so short a volume of text.

or all the movements may constitute a single A bracket. That would work very nicely. But the writer did not leave us enough examples to unravel his thinking on this matter.

This pericope is the "A" section of one of the Gospels' most famous chiasms, an A-B-A' structure that sandwiches the Cleansing of the Temple between the Cursing of the Fig Tree.

 The presence of the supernatural and creation from the OT indicate that there is no support for historicity in this pericope.

The structure of this periocope is a simple chiasm:

This is perhaps the most important single event in Mark outside the Crucifixion, for in many interpretations it triggers the authorities' actions against Jesus. Even when rejected as historical, scholars believe that there is an underlying kernel of history. Therefore it will be analyzed in some detail. There are several reasons to think that the author of Mark invented this story.

First, there is the historical improbability of the Temple Cleansing. The Temple area itself is tremendous in size, more than 12 football fields across and capable of holding tens of thousands of people. Looking at these facts, Paula Fredriksen (2000) has recently explained why she has altered her position on its historical probability:

Price (2003, p295) points out that the Temple covered 35 acres, the size of 34 football fields.

As Josephus notes, there were Roman auxiliaries on call in the Fortress Antonia right nearby. The moneychangers undoubtedly had their own guards and servants, and so did the local priests. It is therefore unlikely that Jesus could have generated an incident there that was prolonged enough for anyone to notice. There were too many warm bodies to squelch it before it got rolling. A further problem, as Buchanon (1991) points out, is that the Temple was not merely the main religious institution of the Jewish religion, it was also the national treasury and its best fortress. The Temple's importance should not be underestimated: all three sides in the internal struggle during the Jewish War fought to gain control of the Temple. Not only is it highly unlikely that Jesus could have simply strolled in and gained control of the Temple, it is also highly unlikely that anyone would have permitted him to leave unmolested after such a performance.

An additional problem is provided by the awkwardness of v17, which has Jesus teaching as he is tossing out the moneychangers. It is almost comic to imagine Jesus shouting out parts of the Old Testament while overturning benches and preventing people from carrying the sacrificial vessels around an area that is thousands of square yards in size. Note that Jesus turns over the tables as if there were only a handful of them, rather than some tables.

David Seeley (2000) notes many of the practical arguments against historicity:

In addition to the commonsense issue of implausibility, as Crossan has noted in The Birth of Christianity, a story may be labeled invented when, on every level, it shows obvious literary derivation. Speaking of the Passion Story, he writes: "The individual units, general sequences, and overall frames of the  passion-resurrection stories are so linked to prophetic fulfillment that the removal of such fulfillment leaves nothing but the barest facts..." (1998, p.521).  The Temple Cleansing is one such story; indeed, the combination of OT creation and Markan redaction leaves nothing at all, not even the barest facts.

At its lowest level, the individual details of the story itself, the Temple Cleansing is composed of two basic strands, one of Markan redaction, the other of OT literary invention. The Temple Cleansing in part is taken from the story of Nehemiah and the Temple, and borrows from it two key details:

First, Jesus overturns the benches of the moneychangers, just as Nehemiah was displeased and threw Tobias' furniture out of the rooms that had wrongly been given to him (Nehemiah 13:9). Troughton (2003, p14) writes:

In the next verse (13:9) Nehemiah returns the sacred vessels back to the rightful place, just as Jesus prevents the vessels from being moved out of the precincts (Mk 11:16). "Nehemiah 13.4-9 details the threat to the Temple cult through accommodation of "foreign influences," notes Troughton (2003, p6), clearly paralleled in Jesus' attack on the merchants as a den of robbers.

Further borrowing of details from the OT is apparent in the key line that Jesus' utters: 'My house will be called a house of prayer for all nations'  But you have made it 'a den of robbers.' -- which combines Isaiah and Jeremiah. The word "robbers" used here is better translated as "insurrectionists." Some have seen a reference to the occupation of the Temple by Jewish Zealots during the siege of Jerusalem in 70 CE. The Jeremiah passage containing 7:11 Mark quoted in v17 is also quoted by Jesus Ben Ananias in Book VI of Josephus Wars. Some exegetes have argued that Jesus may be modeled after Jesus ben Ananias. Earl Doherty (1999, p248-58) has identified other OT cites that may form the basis for this passage, including Malachi 3:1, Hosea 9:15, and Zechariah 14:21.

The other details of the story are redaction of the author of Mark and contain no items of historical value. 

At the next level, the level of intermediate structure, the writer of Mark is again using the OT. The story of Jesus closely parallels the Elijah-Elisha cycle in Kings. Thomas Brodie (1998, p92) explains. At the climax of the two legend cycles, the Temple is cleansed (Jesus drives out the moneychangers, Jehu kills the priests of Ba'al). Both are annointed (2 Kings 9), undergo accession with cloaks on the ground (2 Kings 9), wait before taking over (2 Kings 9:12-13, Mark 11:11), challenge the authorities (2 Kings 9:22-10:27), Mark 11:11 - 12:12), and money given to the Temple (2 Kings 12:5-17, Mark 12:41-44). As Brodie puts it (p93):

At the highest level, the overall story structure, the writer of Mark is again relying on the Elijah-Elisha cycle. Jesus north-to-south movement generally parallels the movements in the Elijah. Where Jesus departs from this movement, so does Elijah. As the EEC narrative approaches Jerusalem, so does Jesus, and the parallels intensify. A second narrative source for this might well be 1 & 2 Maccabees, where in 11:1-9 the writer parallels Simon's entry into Jerusalem in 1 Macc 13, and then in 11:15-19 he parallels the story of Onias III and the Temple vessels in 2 Maccabees.

To sum up:

Markan redactional elements are obvious in "On reaching Jerusalem" (v15) and v18 (the conspiracy and crowd amazement) and v19. The whole passage is typical of the writer of Mark. "Overturning the tables" and "not permitting vessels to be carried out of the courts" are taken from Nehemiah. These two details would not be transmitted by oral tradition; they exhibit clear literary dependence. Hence, the writer of Mark had to have added them via OT construction. Jesus' words cite two different OT authors and cannot be oral transmission; they exhibit literary dependence. The use of the Elijah-Elisha narrative for both the plot of the current set of pericopes and the overall framework of Mark is another example of literary construction that could not have been transmitted. The entire "event" smacks of either Markan redaction or literary dependence on every level. 

Here is the text broken out in detail:

A final knock against this is event is that Josephus does not mention it, nor does Paul (neither Jesus' Temple Cleansing nor his predictions of the Temple's destruction), nor, apparently, did Justus of Tiberias, the historian of Galilee (who does not mention Jesus at all). No source other than the Gospels mentions this event. Paula Fredrikensen (2002) notes:

The structure of this is fairly clear:

Thomas L. Thompson (2005) writes:

The commentary on prayer is set up by the supernatural events of the fig tree. The idea of forgiveness of tresspasses was a common one in antiquity. This pericope completes an A-B-A' chiasm set up by the previous interaction with the fig tree. Because of the presence of the supernatural and the banality of the injunction to forgive, as well as the relationship to Paul, there is no support for historicity in this pericope. 

This entire pericope consists of Markan redaction, with the usual themes of chief priests, scribes, and elders out to get Jesus. It is highly implausible that determined enemies of Jesus would have accepted the answer given in 11:33; it is unlikely therefore that an account of remembered history would simply have broken off without a far longer exchange. The exchange shows a variant on the chreia form, in this case the teacher is shown besting his adversaries with a clever question rather than a clever riposte.

This pericope begins a block of 5 controversy stories that doubles the block of 5 controversy stories in Mark 2 and 3. It is also John the Baptist's last appearance in Mark.

The implausibility of the situation should become apparent if one thinks about the political sensitivity of the question Jesus has just asked: Jesus has just queried the Jerusalem Temple leadership what they think of someone the writer informed us 5 chapters ago was executed by Herod, the potentate of the territory next door, who held his Tetrarchy by Roman largesse. The writer of Mark seems unaware of the political implications of having Jesus asking the Jewish authorities whether they think a recently executed political prisoner was a real prophet. The focus instead is on the source of Jesus' authority.

Mark McVann (1994) reads this as an honor-shame conflict. The Temple's honor, slandered by Jesus' Cleansing of it, must be avenged, and so the authorities challenge Jesus hoping to impugn his status as a true prophet, but instead Jesus shames them. McVann observes that Jesus does this by referring to John's Baptism, which was as insulting to the Temple as Jesus' own acts, since it represented a way for the people to be brought into the community of God without the Temple structure as an intermediary.

The Jesus Seminar (Funk et al 1997) observed:

This pericope is part of a structure that extends into the next chapter;

The implausibility of the situation both from a political standpoint, and the fact that Jesus has just trashed the Temple, as well as the presence of several habitual features of the writer's style, all indicate that there is no support for historicity in this pericope.

Excursus: The Temple-Focused Gospel of Mark

John Paul Heil (1997) writes:

I agree completely. The writer of Mark has a powerful focus on the Temple which he reveals in two ways. First, the writer mentions the Temple in the text of the Gospel itself. The first of twelve uses of word "Temple" in Mark comes in Mark 11:11, when Jesus arrives in Jerusalem. This is followed by several mentions in Jesus' cleansing of the Temple in Mark 11:15-19. In Mark 11:27-33 Jesus is pictured walking in the Temple. Again in Mark 12:35-44 the action takes place in the Temple. In Mark 13:1-31 Jesus makes his famous prophecy of the Temple's destruction. More references follow in Jesus' arrest, trial before the Jewish authorities, and crucifixion. From Jesus' entrance into Jerusalem forward, the Temple is one of the most important threads in Markan discourse.