What to watch for tonight:

1) Turnout. There are 613,521 registered Republicans in Iowa. In 2010, 226,965 voted in the Republican primary. Last cycle’s Republican caucus turnout, with a competitive Democratic primary drawing some of the independents, was about 119,000. With a competitive primary and anti-Obama animus stirring Republicans, turnout should be higher . . . but will it?

2) How does Mitt Romney perform compared to last cycle? Some folks think yesterday’s post laying his 2008 performance as a key threshold is setting the bar too high. But if Romney is a stronger candidate this time around, why shouldn’t he clear 25.19 percent and/or 30,021 votes? (If turnout is higher, it is possible Romney could pass 30,000 votes and still have a smaller percentage of the vote.) Romney had a lot of factors break his way in Iowa — Gingrich choosing to stay positive for so long, the rise of Paul, the infighting among Santorum and Perry. Few if any attack ads focused on Romney’s flaws. If the former Massachusetts governor can’t surpass his second-place finish, it will be the first rattle in the engine of a campaign that is supposed to be humming along smoothly.

3) Assume that the polls are accurate and Romney and Ron Paul finish first and second tonight, relatively close together. The rest of the race might depend on how close together or far apart slots three through six are. Santorum appears ready to have his day in the sun, and could end up enjoying a last-minute surge that scrambles the expectations. Is fourth place good enough for Gingrich? It depends on whether fourth place is 13–15 percent or whether fourth place is 7–10 percent. The same goes for Perry and Bachmann. If they can argue that they were within a few percentage points of third place, they’ll have an easier road ahead than if they have to sustain momentum after finishing in the mid to low single digits. They can and probably will go on after tomorrow, but as Giuliani demonstrated last year, even the biggest-name candidate runs into trouble with enough consecutive bad finishes.