It is a question that must have occurred to many candidates over the years: How can I be losing to this guy?

Two versions of it have been asked of the Republican presidential race: Why doesn’t anyone seem to be able to defeat a front-runner as obviously flawed as Mitt Romney? And why hasn’t Romney been able to score crushing victories against such obviously flawed challengers?

To put both questions together: Why is this field so -- inevitable word -- weak?

The pasting that Republicans took in the elections of George W. Bush’s second term, in 2006 and 2008, made it a thin field from the start. Note that of the three candidates who have won in the primaries -- Romney, Rick Santorum and Newt Gingrich -- the last time any of them triumphed in an election for any office was 10 years ago, when Romney won the governorship of Massachusetts.

Still, there were other Republicans who survived those years and could have run: Haley Barbour, Mitch Daniels, Jeb Bush, John Thune and others. Why didn’t they? There were, of course, specific considerations behind each decision. Daniels let us know that his family objected to a run; Bush is said to think that the nation isn’t yet open to another Bush presidency.

Other calculations would have been common to all of the candidates. On the one hand, President Barack Obama looked beatable during 2010 and 2011, when they would have been mulling it over. Getting the nomination, on the other hand, may have seemed more daunting.

Establishment versus Insurgents

Almost every Republican nomination contest sees a division between establishment-oriented candidates and conservative insurgents. (The great exception in recent decades was in 2000, when the establishment candidate, George W. Bush, faced an insurgent from the left in John McCain.) The balance of power is held by those voters -- sympathetic to both the insurgents and the party establishment -- who describe themselves to pollsters as “somewhat conservative.”

The establishment always wins these fights, for several reasons. Its candidates make the necessary accommodations to stay acceptable to the center of the party. Voters who want a conservative insurgent almost invariably fail to settle on one candidate to play that role. They also sometimes favor candidates who, for one reason or another, just aren’t plausible nominees. These candidates may, for example, never have won a statewide election anywhere, like Herman Cain and Michele Bachmann. Temporary enthusiasm from the pro-insurgent portion of the party can make such candidates appear to be leading for a time, but the party’s sober center always rejects them in the end.

So if you are a would-be contender for the nomination, you have to assemble a winning coalition without the rightmost third of the party, who are going to spend their votes on no-hopers. That means, in practice, you will have to become the establishment candidate yourself. Something like this thought process is what moved Romney, who was one of the conservative insurgent candidates in 2008, to position himself that way this time.

For someone like Thune, the fight against Romney starts to look a lot harder. He has his vulnerabilities, but he has also run for president before. He has a national organization, a national financial network and national name recognition. You have none of these things.

Tim Pawlenty tried to run the kind of candidacy that Barbour, Thune and the others would have run: a campaign designed to be plausible to the party establishment but also a few steps to Romney’s right. But he wasn’t far enough to Romney’s right to excite the anti-Romney insurgent vote, and he couldn’t reach parity with Romney in establishment support. So the Pawlenty campaign died early.

Competitive with Obama

If Romney hadn’t run, it is entirely possible that one of these potential candidates would have entered the race and ended up beating back conservative insurgents more decisively than Romney has. Maybe Pawlenty himself would have done it. But Romney ran, which meant that he would have the establishment slot pretty much all to himself. Republicans were left with a very typical establishment-versus-insurgent contest, but the establishment candidate was weaker than usual.

The primary calendar weakened him further. Jay Cost of the Weekly Standard points out that when McCain won Florida in 2008, he acquired enough momentum to win the Super Tuesday primaries days later. This time, Romney won Florida and saw his polls go up -- and then nothing much happened for weeks. Momentum dissipated.

So here we are. The 2006 and 2008 elections reduced the number of people who could compete in the primary-within-the-primary to be the establishment Republican candidate. Romney crowded out the rest. Well before Iowa or New Hampshire held their contests, he had thus become the likely nominee -- even though he didn’t, and doesn’t, have the affections of the party faithful. His remaining opponents can do well among the party’s “very conservative” voters but have too little appeal to the rest to win majorities themselves.

That’s why the field seems weak. But Romney’s flaws don’t doom him in the general election: Even amid today’s Republican strife, the polls show him competitive with Obama. If Romney wins in November, the field won’t look quite so weak in retrospect.

(Ramesh Ponnuru is a Bloomberg View columnist and a senior editor at National Review. The opinions expressed are his own.)

To contact the writer of this article: Ramesh Ponnuru at rponnuru@bloomberg.net

To contact the editor responsible for this article: Timothy Lavin at tlavin1@bloomberg.net