On the surface, the new (and final) Des Moines Register poll of likely Iowa caucus-goers basically corroborates polling from Rasmussen and NBC/Marist earlier in the week, which showed Mitt Romney slightly edging Ron Paul, while Rick Santorum gained enough ground to move into third place. The numbers are almost identical, at 24/22/15 — but it’s not the topline that is the real news. The four-day poll of 602 likely caucus-goers, which is a larger sample than NBC/Marist but smaller than Rasmussen’s single-day survey, had significant change in the final two days of polling on Thursday and Friday: But the four-day...