In a must-read piece Ramesh Ponnuru explains why the establishment Republican candidate almost always wins the presidential nomination and why Mitt Romney is succeeding. He writes:

Establishment-oriented candidates keep winning for two reasons. The first is that the party establishment has moved to the right, too, co-opting conservatives who might otherwise have overthrown it. . . . The second reason the establishment wins is that its opponents never unify behind another candidate.

As Ponnuru notes, that goes a long way toward explaining Romney’s success. “[Texas Gov. Rick] Perry is running as the conservative candidate, and so he is, as he put it, the pinata at every debate: a target for Romney, but also for Michele Bachmann, Rick Santorum and Herman Cain. The funny thing is that even though Romney is running as the ‘moderate,’ rather than the ‘conservative,’ in the race, his actual positions are to the right of the ones he had in 2008. For example, he signed a pledge to oppose raising the debt ceiling until Congress passes a Balanced Budget Amendment. Like previous successful establishment candidates, he is placating the party base.”

I suggest there are a few other factors helping Romney. First, let’s not forget all the establishment candidates who didn’t run — Indiana Gov. Mitch Daniels, New Jersey Gov. Chris Christie, Mississippi Gov. Haley Barbour, Sen. John Thune (S.D.), and Rep. Mike Pence (R-Ind.). Had any of them gotten in, Romney’s support would have fractured, and he could well be far back in the pack.

Second, Romney is simply a better candidate at this stage than his opponents. We forget that 90 percent of politics (like sports) is preparation and execution. For Romney, that translates into polished policy roll-outs, articulate debate performances and virtually no errors. Compare that to the gaffe-prone Rep. Michele Bachmann (R-Minn.) or the controversy-plagued Perry.

Third, the overriding issue is the economy, not health care and certainly not any social issue. From the get-go, Romney advisers were candid: If the race is only about health care, he loses; if it is about other things, he’s likely to win. As it turned out, the race is almost exclusively about the economy. (Hence the economy-only debate tonight.)

And finally, President Obama’s vulnerability, in large part a function of his perceived ineptness and lack of management skills, has boosted the candidate who projects stability, competence and mastery of economics. The sense that the country is careening out of control has, ironically in the Tea Party era, diminished the allure of candidates heavy on rhetoric and low on concrete policy proposals. That in part explains why Perry’s Social Security rhetoric tripped him up. A majority of voters, even in the GOP primary electorate, are looking for a conservative reformer, not a bomb thrower. And most of all, they are looking for the candidate who can beat Obama in the general election.

None of this is to suggest that Romney has the nomination in the bag. Cain could effectively wipe out residual support for Bachmann, Perry, Santorum and others, thereby consolidating the entire anti-Romney vote. Romney could falter in Iowa, falling victim to high expectations. Cain could show greater fluency on the issues and project authority on foreign policy. But for now, none of these things has happened. So it is Romney’s race to lose.