Mitt Romney lost in 2008 to Mike Huckabee because Brownback dropped out. With Brownback gone, his supporters went to Huckabee and Huckabee won the support of religious conservatives and thus the state.
Of course a number of religious conservatives back Newt, Paul, and Romney. However, 3 candidates are now staking their campaigns on the support of religious conservatives: Santorum, Bachmann, and Perry. These 3 campaigns have gone all-out for religious conservatives and combined have enough support to win Iowa. Seperate, however, they fall short.
For the Iowa Straw Poll, Bachmann won because Santorum was lower in the polls and Perry was not in the race. Were Perry in the race when the straw poll took place, Bachmann would not have won... Paul would have.
For all the changes in Iowa polling, things have not changed. The combined support of Bachmann, Santorum, and Perry is the same as it was at the time of th staw poll. It is just divided into 3 candidates. This has been Romney's plan, and it is working.
The key question that Bachmann, Santorum, and Perry face is can they win supporters from one or both of the other candidates? The answer thus far has been no. 2 of those 3 candidates will not agree to drop-out and support the other prior to Iowa. Bachmann and Santorum have no means to lauch attacks on the other two to eliminate them from the race. Perry's targetting all his add money on Gingrich. Simply put, they will likely each get about 10% for the Caucus. A sort of mutually-assured-destruction; each staying in the race and taking the supports the other needs to win.
Romney's next line of attack was destorying Gingrich, which appears to be going well enough for Romney that Paul is now ahead in Iowa.
So, a win by Paul, followed by a win by Romney in NH....the race is looking good for Romney.