For Republicans, the presidential primary contest has become a nightmare from which they can’t wake up. Their front-running candidate cannot close the deal; their runners-up cannot surge sufficiently to displace the front-runner. Each candidate’s favorability rating has drooped as the campaign rolls on. None has been able to broaden his support beyond a relatively narrow base. The prospect that no candidate will amass a decisive majority of delegates well before the party’s August convention looks increasingly plausible.

Mitt Romney is winning small. He has shown strength in New England and the Mormon West but eked out narrow victories in the industrial Midwest only by vastly outspending his opponents. (He remains weak in the party’s base region: the South.) He continues to do well among affluent voters but loses working-class households to Rick Santorum. In a one-on-one match Tuesday with Ron Paul in Virginia, Romney won by only a 60-40 split, though Paul was nowhere to be found in the commonwealth, or on its airwaves, during the week leading up to the vote.

It’s not as if Romney is having trouble dispatching the likes of Dwight Eisenhower or Ronald Reagan. Santorum and Newt Gingrich have been decisively repudiated by voters (Santorum in 2006) or their own peers (Gingrich). And weak as his opponents may be, their campaigns are even weaker. Gingrich and Santorum failed to make the ballot in Virginia, and Santorum has failed to find enough delegates to fill up his slate in such key states as Ohio and Illinois.

The fact that none of Romney’s opponents had turned up the July 2009 op-ed he penned for USA Today, in which he called for a national health insurance plan that included an individual mandate — a column that all but neutralizes any Romney attack on Obamacare — is further confirmation that their campaign operations are stunningly incompetent. (The column was unearthed last week by reporter Andrew Kaczynski of Buzzfeed.) Yet blessed by marginal opponents and a surfeit of funds, Romney still has not won the votes of enough Republicans to lock up the nomination.

For his part, Santorum wins the support of his party’s most conservative voters and the downscale ones, but he has yet to prevail in the more prosperous suburbs. He’s done well in the Plains states and the upper South. But he continues to lose conservative votes to Newt Gingrich. Santorum needs to defeat Gingrich in the Alabama and Mississippi primaries next week if he is to have any chance of bumping Newt out of the race and picking up the bulk of his supporters.

Super Tuesday was actually near-disastrous for Gingrich: Though he won his home state of Georgia, he failed to finish even second in any of the nine other states that held elections. He came in fourth, behind Paul, in five states. Gingrich’s role as the primary season winds on has been reduced to depriving Santorum of the votes the former senator needed to best Romney. (Indeed, you have to wonder if Sheldon Adelson — a casino operator who knows how to play the odds — keeps funding Gingrich’s super PAC to help Romney beat Santorum.)

If Romney can’t claim enough delegates going into the convention to secure his party’s nod, he may end up compelled to strike deals that damage his already weak general-election prospects. His standing with Latino voters (whom he has offended with his hard line on undocumented immigrants and the Dream Act) is abysmal — a Fox News poll released Monday showed Romney trailing President Obama by a mind-boggling 56 points (14 percent to 70 percent). Given that, Romney might help himself by making Sen. Marco Rubio (R-Fla.), a Cuban American, his running mate. (It would certainly help him win Florida.) But if he chugs into Tampa still a dollar short of delegates, Romney might come under pressure to pick Santorum, or even Kentucky Sen. Rand Paul (Ron’s son), in return for the votes that put him over the top. Either one would further marginalize the ticket — and do nothing to help Romney win more Latino support.

At bottom, the weakness of this year’s Republican field is chiefly a refraction of the weakness of the Republican electorate. Republicans want a candidate who channels their rage at Obama and the unfamiliar America — economically stagnant and increasingly multi-racial — over which he presides. They want a candidate who will turn the clock back to the economics, demographics and verities of an earlier — if needs be, mythic — time. These are not tasks that serious leaders embrace. In the absence of serious leaders, we have Romney, Santorum, Gingrich and Paul.