WASHINGTON (AP) - Mitt Romney seems firmly in command in a Republican presidential field that hasn't figured out how to stop him.

Twelve weeks before the first party voting, the GOP establishment is coalescing around the former Massachusetts governor. He has more campaign experience, money and organization than anyone else. He showed again this week that he's the best debater in the bunch. And President Barack Obama's campaign is treating him almost as the presumptive nominee - even though Romney still faces challenges in some early voting states.

The biggest question in Republican circles is when and how Texas Gov. Rick Perry will use his own substantial campaign funds to buy TV ads hitting Romney's record on health care, abortion, gay rights and job creation.

Perry's campaign, which seems best-positioned to challenge Romney, dropped broad hints Wednesday that the moment is near.

"Now that the field is full, the air war will start soon," said Katon Dawson, former chairman of the South Carolina GOP and Perry's top adviser in the state. "We seem to be inside a 100-day window," Dawson said. "Governor Perry will be extremely competitive on the air."

The tone is different up the coast in New Hampshire. Among rank-and-file Republicans there, even those who favor other candidates have a sense that Romney has gained an air of inevitability. "It's very frustrating," said state Rep. Jim Waddell, of Hampton, who backs former Utah Gov. Jon Huntsman.

Some go even further about Perry's recent drop. "In New Hampshire, he certainly is done," said GOP state Rep. Keith Murphy, who is uncommitted in the race.

Perry's advisers say there's plenty of time to overtake Romney in key states. They are frustrated by bad reviews of the Texan's debate performances, including Tuesday's in New Hampshire. They say it's Romney who is ripe for sharp criticism of his revised positions on abortion, gay rights and gun control, all now markedly more conservative than in the 1990s and early 2000s.

In the debates so far, Perry has generally fallen flat when hitting Romney's "flip-flops" and the health care initiative that required Massachusetts residents to obtain medical insurance. Perry's advisers say aggressive TV ads will do a far more powerful job.

Although Republican and Democratic insiders see Romney as the front-runner, several signs give Perry and the other rivals hope. Most Republican polls show Romney falling well short of a majority of support, as restless voters consider one alternative after another.

Rep. Michele Bachmann of Minnesota surged in mid-summer, then fell as Perry briefly soared. In recent polls, former pizza company executive Herman Cain has ranked as Romney's top rival, although few campaign strategists believe he will be the nominee.

An NBC-Marist College poll in Iowa found that tea party supporters prefer Cain. In national polls, combined support for Cain, Perry and Bachmann exceeds Romney's support.

National polls matter less than surveys closer to home in a handful of early voting states, including Iowa, New Hampshire and South Carolina. Many campaign strategists say Perry must win the Iowa caucus, or at least far outdistance Romney there, to survive the New Hampshire primary, where Romney is favored.

The next states to vote will be Nevada, where Romney seems strong, and South Carolina, where Perry hopes evangelical Christians will back him.

In Iowa, Romney continues an under-the-radar strategy designed to keep expectations low while positioning himself for a possible late surge. Four years ago Romney poured huge sums of money and time into the state, then suffered a crushing loss to Mike Huckabee.