The best article I’ve read on the Republican presidential primary never mentions Mitt Romney’s name. Nor is it about Herman Cain or Rick Perry. In fact, it’s not about the presidential candidates at all. It’s about the party they’re trying to win over.

“As we theorize,” write the half dozen political scientists who collaborated on “A Theory of Political Parties,” published this year, “parties no longer compete to win elections by giving voters the policies voters want. Rather, as coalitions of intense policy demanders, they have their own agendas and aim to get voters to go along.”

You can debate whether a more benign model of political parties, which the authors believe has been supplanted, ever really existed. But there’s little doubt that their more cynical take is a persuasive description of politics as it is practiced today. As they see it, political parties are basically groups of people with intense policy preferences who are trying to figure out how much they can get away with. But you can’t get away with anything if you don’t hold office. So the basic work of political parties is figuring out precisely how much of their agenda they need to sacrifice on the altar of electability.

“Voter inattentiveness creates the opportunity for intense minorities to pursue their narrow goals,” the authors write. “But it also creates uncertainty about just what it takes to win an election. Parties work hard to figure out ways to increase the chance that voters will respond positively to them, but basic uncertainty about how the inattentive majority will vote is a persistent feature of electoral politics.”

A Republican Dilemma

That basically explains the dilemma the Republican Party faces right now. Its members sense that this election might end with Republicans controlling the House, the Senate and the presidency. In that event, Republicans could get away with quite a lot. So they don’t want to blow it. What a shame it would be to have wasted this opportunity on a centrist candidate who will just end up compromising with Senate Democrats and looking to burnish his image with independents. On the other hand, it would be even worse to blow the opportunity on an extremist candidate who will scare voters into re-electing President Barack Obama.

At the end of October, the National Journal polled 105 Republican insiders and asked who they expected would win their party’s nomination. Romney got 98 percent of the votes. Similarly, the Intrade political betting markets give Romney a 70 percent chance of capturing the Republican nomination. He is the only Republican who is consistently competitive with Obama in national polls.

Yet Romney has not, at any point, secured a commanding lead in the Republican primary campaign. The website averages polls of the Republican field to smooth out the statistical noise. The former governor of Massachusetts has not once cracked 30 percent. Perry, by contrast, reached 32 percent in September, before his numbers collapsed. Cain is leading now. So what gives?

Well, the Republican Party. “Parties must still, as in existing theory, respond to voter wishes, but they wish to cede as little policy to voter preferences as possible,” the political scientists said. With Romney, Republicans worry that they will cede too much to voter preferences. This is the same Romney, after all, who was once pro-choice, who supported an individual mandate for health care in Massachusetts, who declared man-made global warming a fact. As I’ve argued before, that record of ideological flexibility is, in some ways, Romney’s great advantage: It makes him acceptable to independent voters even as he panders relentlessly to the conservative base. It encourages independents to explain away his most extreme positions as mere expediency.

Discounting Romney

But that record also encourages the party’s conservative base to discount Romney’s most extreme positions as, well, mere political expediency. They would prefer a candidate who they know they can trust. But the search for a not-Romney hasn’t gone well. Perry proved a weak campaigner with a worrying penchant for threatening the chairman of the Federal Reserve in public. Tim Pawlenty was a bore. Michele Bachmann caught fire in Iowa — but not for long. Cain can’t explain his tax plan or recall his sexual harassment payouts. And Representative Paul Ryan and Governors Chris Christie and Mitch Daniels passed on the race.

So the Republican Party is left with candidates who are too ideological to be elected and a front-runner who isn’t ideological enough to be trusted. Making matters worse, voters are likely to pay particularly close attention to this election. With an economy this bad, there’s no chance that they’ll tune out, as they did in 2000. Then, peace and prosperity lulled the electorate into complacency, and George W. Bush was able to present himself as not all that different from Al Gore. The Republican Party got away with quite a lot in ideology that year without sacrificing electability. This year, Republicans can’t.

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Follow Ezra on Twitter @ezraklein. Ezra Klein is the founder and editor-in-chief of