WASHINGTON – It’s been a wild ride, but the storyline of the Republican race remains remarkably simple and constant: It’s Mitt Romney and the perishable pretenders.

Five have come and gone, if you count the Donald’s aborted proto-candidacy. And now the sixth and most plausibly presidential challenger just had his moment – and blew it in Michigan.

It’s no use arguing that Rick Santorum won nearly as many Michigan delegates as Romney. He lost the state. Wasn’t Santorum claiming a great victory just three weeks ago when he shockingly swept Missouri, Minnesota and Colorado – without a single convention delegate being selected?

He was right. It was a great victory. Delegate counts were beside the point. These three wins instantly propelled him to the front of the field nationally and to a double-digit lead in Romney’s Michigan backyard.

Then Santorum went ahead and lost it. Rather than sticking to his considerable working-class, Reagan-Democrat appeal, he kept wandering back to his austere social conservatism. Rather than placing himself in “grandpa’s hands,” his moving tribute to his immigrant coal miner grandfather as representative of the America Santorum pledges to restore, he insisted on launching himself into culture- war thickets: Kennedy, college and contraception.

He averred that John Kennedy’s 1960 Houston speech on separation of church and state makes him “throw up.” Whatever the virtues of Santorum’s expansive view of the role of religion, the insulting tone toward Kennedy who, living at a time of frank anti-Catholic bigotry, understandably offered a more attenuated view of religion in the public square, was jarring, intemperate and utterly unnecessary.

As was his sneering at President Obama’s wanting to open college to all. Santorum called that snobbery and an attempt at liberal indoctrination. Sure, there’s a point to be made about ideological imbalance in higher education and about the dignity of manual labor. But to do so by disdaining the most important instrument of social mobility – one that millions of parents devoutly desire for their children – is simply bizarre.

Finally, the less said about contraception the better, a lesson Santorum refused to learn. It’s a settled question. The country has no real desire for cringe-inducing admonitions from politicians about libertinism and procreative (versus pleasurable) sex.

The result of these unforced errors was Santorum’s Michigan slide. His post-trifecta lead vanished. He forfeited a victory that would have shattered the Romney candidacy.

Santorum knows why. He’s now recanted the Kennedy statement. And remember that odd riff with which he began his Michigan concession/victory speech? About three generations of Santorum women – mother, wife, daughter – being professional, strong, independent, i.e., modern? That was an unsubtle attempt to update his gender-relations image by a few decades.

Too late. Among men, Michigan was essentially a dead heat. But Santorum lost women by five percentage points – and, with that, the race.

Social issues are what most deeply animate Santorum but 2012 is not the year they most animate the electorate. In Michigan, among those for whom abortion was the most important issue, Santorum won by a staggering 64 points. But they made up only 14 percent of the electorate. Seventy-nine percent cared most about the economy or the deficit. Romney won them by 17.

And, of course, he won overall. But only by three points, a weak showing in Romney’s native state where his (former governor) father is legend and where Romney outspent Santorum 2-to-1.

The result should never have been that close. Romney won by default. Santorum had a clear shot and simply missed his mark.

It’s not over. Super Tuesday could scramble the deck. But once again, the smoke clears and Romney remains – slow, steady, unspectacular. The tortoise in the race, dull and methodical, with an awkward, almost endearing (note: almost), stiffness. In short, a weak front-runner in an even weaker field.

Hence the current Republican gloom, the growing Democratic cockiness. But the game is young. True, given the national mood and the state of the economy, Republicans should be far ahead. They’ve blown a significant lead. But the race is still 50-50.

Romney remains the presumptive nominee. His Michigan victory speech was jaunty, sharp and good. He’d advanced a serious plan for tax and entitlement reform four days earlier. Now he needs to (1) bite his tongue anytime the temptation arises to riff about class, money or cars (Cadillacs in particular), (2) ask George Bush 41 the proper way to eat pork rinds, (3) pray for yet more luck, the quality Napoleon famously valued in his generals above all others.

© 2012, The Washington Post Writers Group