Mitt Romney’s ceiling in Iowa doesn’t look like glass. It looks like reinforced concrete.

Even after three conservative candidates rose and fell in polling in Iowa, the former Massachusetts governor still can’t get above the 25 percent mark in the crucial early caucus state. “That really says something about how low his ceiling is,” one GOP consultant told me recently.

More than 10 months ago, I wrote a column saying the obvious: that although Romney was leading the GOP contest and had plenty of assets, he also had so many liabilities that it was unclear whether he could win the Republican nomination. 

But given the early exit of former Minnesota Gov. Tim Pawlenty and the decision of other potentially formidable candidates to take a pass, it’s stunning that Romney has been unable to increase his support at all over the past year.

And now, Republican insiders are asking what must strike many as the oddest of questions: What can Romney do now to try to stop Newt Gingrich and win his party’s nomination for president?

GOP insiders note that Romney has built the best national organization and continues to have a financial advantage in the race.

But organization may not be what it once was in presidential politics. Certainly it isn’t as crucial as it once was in Iowa. While Romney had by far the best organization in Iowa four years ago, it was former Arkansas Gov. Mike Huckabee, a relatively late entry into that race, who relied on momentum to win the caucuses.

This cycle, polling suggests that organization isn’t driving sentiment in Iowa. How else can anyone explain how candidates with little or no organization in the state have surged in surveys of likely caucus attendees? The GOP debates seem to be trumping (or at least overshadowing) the Iowa ground game.

The question is: When primaries and caucuses come in bunches, not simply one at a time, will Gingrich be able to compete in all of them?

Barack Obama shocked Hillary Rodham Clinton in 2008, in part, by paying attention to caucus states that Clinton was ignoring. Could Romney do the same because of the breadth of his organization?

Possibly, but it would be much more difficult for him. After all, Obama was a unique figure who generated grass-roots excitement. Romney hasn’t excited anyone, and his great appeal is that because of his experience, style and broader electoral appeal, he is a “safe” choice.

Romney also seems likely to have a substantial long-term financial advantage in the contest. The former governor hasn’t spent heavily on TV yet, instead preferring to husband his resources for a long contest.

But television, as one strategist pointed out to me recently, is less important in a presidential race than in a Senate or House race. The presidential race will get plenty of “earned media,” so voters will have the information they need to make decisions without relying on paid TV ads.

The calendar presents some problems but also a few opportunities for Romney.

All five of the first primaries (New Hampshire, South Carolina, Florida, Arizona and Michigan) are likely to suffer a 50 percent penalty because they violated “windows” established by the Republican Party and amended by the Republican National Committee in August 2010. That doesn’t mean they will lose importance, however.

Obviously, Romney must win an early test, and the most likely one — indeed, the only one — is New Hampshire.

The rules require primaries scheduled for March (currently there are 11 of them, though Texas could end up moving back) to use proportional representation. That could make it difficult for one candidate to lock up the nomination early.

A long race could be key for Romney, but not because of his organization or money. Rather, a long race would keep Gingrich under the microscope, giving Republican primary voters more time to focus on his record and giving Gingrich more opportunity to self-destruct.

But there is no guarantee that Gingrich will implode, at least before the GOP’s Tampa convention, or that Romney can get enough support during the process to derail the former Speaker. And while the idea of a late entry into the race or a brokered convention doesn’t seem quite as outlandishly silly as it usually does, Iowa and New Hampshire are likely to separate the wheat from the chaff in the GOP race.

Part of Romney’s problem is that conservatives simply don’t trust him and so far are not giving him the benefit of the doubt. They are giving it to Gingrich, whose record seems no more conservative than Romney’s.

At a time when grass-roots Republicans yearn for a political outsider as a nominee, they are turning to Gingrich, a longtime Member of Congress and one-time House leader, rather than Romney, who has never held federal office or served in D.C.

One veteran Republican explains the odd situation by suggesting that conservatives seem to have more of a “cultural connection” with Gingrich than with Romney, much as they did with Ken Buck rather than Jane Norton (two equally conservative Republicans) in the 2010 Colorado Senate primary or Rand Paul rather than Trey Grayson in the 2010 Kentucky Senate primary.

Can Gingrich be stopped? We will see. The next month will offer many answers.

Wisconsin Rep. Paul Ryan’s recent criticism of the former Speaker could be a serious blow to Gingrich. Ryan is an icon to many conservatives, and his negative comments about Gingrich could constitute a new and potentially effective front against the former lawmaker.

Republicans who fear Gingrich — either because they find him untrustworthy and erratic or because they believe he damages his party’s prospects substantially in 2012 — must continue to slam the former Speaker, painting him as Obama’s best chance for winning a second term.

But ultimately, Gingrich’s prospects may well depend most on his own performance and on his ability to continue to appeal to conservatives across the country. In the past, Gingrich has proved to be his own worst enemy.

Stuart Rothenberg is editor of the Rothenberg Political Report.