The Republican Party’s inevitable decision to nominate Mitt Romney for president is starting to look evitable after all.

That’s certainly not a consensus view among the Washington cognoscenti, who tend to see the yet-to-come primaries and caucuses as mere formalities. Romney, they say, is the GOP’s obvious choice — a poised and experienced candidate with presidential bearing, world-class hair and the ability to speak in complete sentences, even about the economy. Sooner or later, the party will come to its senses and see that he has the best chance of beating President Obama.

The White House certainly seems to buy into this scenario. For months now, virtually every conversation I’ve had with one of those increasingly chatty “senior administration officials,” on any subject, has included at least a swipe or two at Romney. It’s clear that he’s the opponent the Obama machine is gearing up to face.

But I’m less and less convinced. It’s hard for me to see how any of the other candidates can win the nomination — but it’s hard for me to see how Romney wins it, either.

Polls have told a consistent story: Between 20 percent and 30 percent of Republican voters support Romney, and the rest support somebody else. Actually, not somebody, anybody.

It was bad enough when Romney’s main challenger was Michele Bachmann, whose views are so extreme that she favored allowing the nation to go into default — thus triggering the possible collapse of the global financial system — rather than to raise the debt ceiling. It was bad enough when Rick Perry entered the race and vaulted into the lead, sight unseen. It was bad enough when Republicans, having actually made Perry’s acquaintance, practically offered New Jersey Gov. Chris Christie the nomination, along with a dog and pony, if he’d just say yes.

But the whole Herman Cain infatuation is much worse, from Romney’s point of view. Here’s a man with no experience in public office, no knowledge of international affairs and, from the evidence of his “9-9-9” tax plan, bizarre ideas about how arithmetic works. Yet before allegations of sexual harassment threatened to derail the Cain Train, he was leading in many polls.

It is safe to conclude that most Republicans are looking for an alternative. Clearly, theydon’t see Romney as the inevitable nominee — and they’re the deciders.

Mostly, they don’t trust his bona fides as a party-line conservative. And indeed, his record gives them reason to doubt.

The latest evidence came Thursday in a Washington Post story quoting advocates for several liberal causes about their interactions with Romney when he was running for and serving as governor of Massachusetts. According to the individuals quoted, Romney portrayed himself as someone liberals could work with on causes such as abortion rights, gay rights and protecting the environment — and as a “good voice” to help soften the Republican Party’s hard-line stances on these issues.

Today, Romney espouses orthodox GOP positions. He describes himself as unambiguously anti-abortion. He is firmly against gay marriage. And while as recently as June he said he believed humans contribute to global warming, he now says, “We don’t know what’s causing climate change on this planet.”

He certainly doesn’t sound like a moderate anymore. But some Republican ears hear the whoosh of wind whistling past a weathervane.

You can’t beat somebody with nobody, however, and thus far the contenders who played the role of “Not Mitt Romney” have all had brief runs. It’s reasonable to assume that if the pattern holds, all Romney has to do is carry on — he has plenty of money and determination — and eventually the party will fall in line, if not in love.

Sounds reasonable, but not inevitable.

The most obvious alternative is a Perry comeback. His poll numbers have nowhere to go but up, and his fundraising prowess — $17 million last quarter — can allow him to be the last “Not Mitt” standing after others go broke and drop out. His hair is every bit as presidential as Romney’s, although he’s still working on the part about speaking in complete sentences.

The other possibility is a leap of faith.

It’s hard to imagine that any of the other candidates can seriously challenge Romney or that some new contender could enter the race. But did anyone think the words “Herman Cain” and “front-runner” would ever appear in the same sentence? So far, the conventional wisdom hasn’t been very wise at all.

eugenerobinson@washpost.com