Posted on the door are the office's hours -- 10 a.m. to 9 p.m. -- and on any given night 20-odd volunteers cram into the compact strip-mall suite, situated between a nail salon and a Quizno's, to phone-bank for Paul and identify Paul supporters.

They are building quite a list.

Paul's campaign has identified 20,000 committed supporters for the caucuses, Iowa insiders say. (For strategic reasons, the Paul campaign will not confirm or deny this figure.) If that's true and caucus turnout matches 2008's all-time high of 119,000, that's good for 17 percent; if turnout is 100,000 or lower, as most experts expect, Paul would have 20-plus percent of the vote already locked up.

Four years ago, Paul's campaign was a ragtag band of idealistic rebels. A mostly nonprofessional operation of largely self-organizing grass-roots supporters was enough to get him 10 percent of the vote in Iowa and 8 percent in New Hampshire.

This time around, it's a very different story. In Iowa especially, Paul's campaign has built a sophisticated voter turnout machine. With its intensely dedicated core of youthful followers recruiting non-party regulars to the caucus electorate, it is reminiscent of nothing so much as Barack Obama's 2008 Iowa campaign, which was his springboard to the Democratic nomination.

"It is vastly different than four years ago," said Spiker, a realtor from Ames who sits on the state GOP Central Committee. "We have a professional staff now who know what to do and are better able to direct all the energy of the volunteers." For example, instead of standing on corners waving signs -- something Paul supporters are well known for, but which has little impact on voters -- volunteers have been put to work going door to door in their communities.

Paul's ability to bring out non-traditional caucus-goers also carries echoes of Mike Huckabee's successful 2008 Iowa campaign, which rallied many evangelical Christians who weren't previously politically active.

"If anybody's bringing new people out this time, it's Ron Paul," said Christopher Rants, a former speaker of the state House of Representatives who supports Mitt Romney. "Last time, it was Mike Huckabee."

It's become clear that Paul's push is having an effect.

"Paul is the only candidate consistently growing and going forward in every poll," said Des Moines-based pollster J. Ann Selzer. In three consecutive Des Moines Register surveys beginning in June, Paul's share of the vote has gone from 7 percent to 12 percent to 18 percent in late November. Paul took second place to Newt Gingrich's 25 percent in that poll, but Gingrich has seemed to slide in recent weeks -- thanks in part to relentless attacks on him by Paul's campaign.

"Ron Paul will finish no lower than a very close third," said Iowa conservative radio host Steve Deace. "His organization is one of the best political organizations in Iowa. The only two politicians with a better organization in Iowa are Tom Harkin and Charles Grassley," the state's two U.S. senators.