In this cycle, that question applies to, well, everyone except Mitt Romney, whose support has been consistent if not impressive in primary polling.  Romney has clearly failed to engage the enthusiasm of the Republican base, which wants a more conservative candidate, as well as hoping for another quality they find missing in Romney.  In my column for The Week, I point out the common thread of the boomlet candidates, and explain why Newt Gingrich’s rise might be the candidate that fits that quality best:

One might be tempted to just dismiss the latest boomlet for Gingrich as a simple matter of waiting his turn, but it is almost certainly more than that. The previous boomlets favored candidates with one quality in common — their perceived enthusiasm for fighting Barack Obama. Tim Pawlenty never caught fire in part because of his easygoing personality, and Jon Huntsman’s track record of working in the Obama administration makes him a suspect candidate, both as a fighter and on policy.

Gingrich, on the other hand, is not just a fighter, but a brilliant fighter. He has used the debates to put his encyclopedic knowledge on display in every aspect of policy. Instead of trying to scale the polling heights by fighting his fellow Republicans, Gingrich has aimed his rhetorical guns at Barack Obama and the national media, the two biggest targets for the Republican grassroots. He dressed down CBS moderator Scott Pelley in Saturday’s debate on a question about killing Americans who join terrorist networks against whom Congress has already authorized military action. Those who want a fighter know that they can trust Gingrich not to embarrass them through incoherence or ignorance, and that he has a more natural inclination to confrontation than Romney.

That won’t make Gingrich an instant hero to conservatives.  As I note in the introduction to the column, Gingrich can be described — with some justice — as the antithesis of a Tea Party candidate.  He has dwelt in the Beltway for decades, which is also one of his strengths in policy acumen, and has committed a number of heterodoxies, if not outright heresies, over the years. Gene Healy at the Washington Examiner makes the (mostly) legitimate, comprehensive case against Gingrich:

In 2003, Gingrich stumped hard for President George W. Bush’s prescription drug bill, which has added about $17 trillion to Medicare’s unfunded liabilities. “Every conservative member of Congress should vote for this Medicare bill,” Newt urged.

And in his 2008 book “Real Change,” he endorsed an individual mandate for health insurance.

In a 2006 piece for Human Events, Gingrich offered House Republicans “11 Ways to Say: ‘We’re Not Nancy Pelosi.’ ” Point seven proposed a Solyndra-on-steroids industrial policy devoted to “developing more clean coal solutions, investing in a conversion to a hydrogen economy” and more. It’s not clear why the former madame speaker would complain.

It’s also unclear why anybody looking to distance himself from Pelosi would plop down on a love seat with her to call for government action on climate change — as Gingrich did in a 2008 television commercial.

It was a season of bipartisan chumminess for Newt. “Kerry and Gingrich Hugging Trees — and (Almost) Each Other,” the Washington Post described a 2007 global warming event Gingrich headlined with Sen. John Kerry, D-Mass.

Later, the Cato VP describes Gingrich as having “a zany, almost Cliff Clavin aspect to his intellect,” which is a little mystifying, given the demonstrated depth of Gingrich’s policy knowledge.  Even when trailing badly in the polls, Gingrich has owned the debates.  If he has had a clunker or two for ideas, spread over three decades, it doesn’t amount to a “Cliff Clavin” level of expertise.  With that exception, Healy makes a pretty good case why Gingrich has failed to catch fire … until now.

So why have voters taken a new look now?  After watching the other boomlet candidates implode due to incoherence, ignorance, and hyperbole, voters may want to get a candidate that makes them feel secure about expertise in both policy and the ability to argue it.   Of the boomlet candidates, only Bachmann filled the bill as a down-the-line conservative anyway; Cain supported TARP, for instance, and Perry has a big problem with crony capitalism to go with his job-creation story.  Bachmann proved unreliable at maintaining credibility with her tendency to overshoot rhetorically and get herself in trouble, and her attacks on fellow Republicans may have also backfired a bit, too.

Gingrich may not be a conservative dream candidate, but he has worked with grassroots conservatives far more than Mitt Romney has over the last several years, and he shows a much greater tendency to fight than Romney does as well.  If there are no reliable conservatives whom voters can trust not to make fools of themselves in a long campaign, Gingrich at least fills that bill.  And compared to Mitt Romney, Gingrich may well be conservative enough to become a rally point — much like Romney himself was in 2008, albeit too late to stop John McCain from winning the nomination.