Only registered Republicans can vote in the Iowa caucuses, but anyone eligible to vote or even registered with another party can decide to register as a Republican on Tuesday evening and participate in the caucuses.

“I think we could have record caucus turnout, and I think that could be in large part with people who had affiliated themselves as independents and now will affiliate themselves as Republicans,” said Iowa Secretary of State Matt Schultz (R), who is supporting former Pennsylvania senator Rick Santorum .

It’s not an insignificant question. How many independents (and even Democrats) decide to cross over may well determine whether Texas Rep. Ron Paul can win.

Paul’s support base is a patchwork of libertarian-minded Republicans and independent voters drawn to his non-interventionist foreign policy views and distrust of the federal government. A surge in same-day registration tomorrow would, presumably, be a very good thing for Paul.

Recent polling in Iowa suggest Paul does very well with voters unaffiliated with either party. In the most recent Des Moines Register poll the libertarian-leaning congressman won 42 percent of unaffiliated voters, with Romney well behind at 19 percent.

“There's a very real chance that Mitt Romney will actually win the Republican vote on Tuesday night but lose the caucus because of Paul's overwhelming support from independents and Democrats,” said Tom Jensen of Public Policy Polling, which estimates 20 percent to 25 percent of caucusgoers will be non-Republicans.

Only 12 percent of GOP caucusgoers said they identified as independents in 2008. But according to pollster Ann Selzer, who runs the Des Moines Register’s poll, entrance polls tend to understate the number of independent voters.

“Our final polls of Republican likely caucusgoers in both 2000 and 2008 were at or near 20 percent,” she said. “I see a bump over the entrance poll from 2008, but not a big bump.”

The problem for pollsters is calculating just how high independent turnout will go. The Register poll included independents, while the CNN survey limited their sample to only registered Republicans.

Yet despite the lack of independents, CNN’s numbers are not significantly different from the Des Moines Register results.

In the CNN poll Romney leads Paul 25 percent to 22 percent, with Santorum at 16 percent. The Des Moines Register has Romney at 24 percent to Paul’s 22 percent and Santorum’s 15 percent. In Public Policy Polling, the numbers are a bit different, but still a suggest a photo finish. Paul is at 20 percent, Romney at 19 percent and Santorum at 18 percent. 

In the most recent Washington Post-ABC News polling, only 11 percent of all potential GOP caucusgoers were registered as "No Party," the state's equivalent of independent — no different from in 2008. Sixteen percent of the likeliest caucusgoers are non-Republicans.


GOP hopefuls launch final assault in Iowa

Where the candidates are campaigning

Romney edges out Paul in new Iowa poll