“Oh no, no, no,” said the energetic young man when I asked him his name and where he was from. He was working the crowd at last week’s Conservative Political Action Conference in Washington.

“Just say I’m a public-spirited person with an important warning.”

Which is?

He raised a bony finger.

“Beware Mitt Romney!”

And then he was gone, vanished in the labyrinthine exhibition hall filled with booths for the National Tax Limitation Committee, the Leadership Institute — “For Conservatives Who Want to Win!” — stophernow.com, Working Families for Wal-Mart, and dozens of others.

All the young man left me with was a pair of foam slippers, flip-flops the lurid color of a crossing guard’s vest. These were meant to illustrate the former Massachusetts governor’s growing reputation as — you’ll never guess — a flip-flopper.

“Romney: Where will he stand in 2009?” I read from the heel.

The fine print told me that in 1992, Mr. Romney voted for Paul Tsongas, a Democrat, for president.

Worse, it reported that in 1994, running against Senator Kennedy, Mr. Romney bragged, “I was an Independent during the time of Reagan-Bush. I am not trying to return to Reagan-Bush” — a repudiation that most CPAC attendees would rank up there with the apostle Peter’s in the wee hours of Good Friday.

And, finally, Mr. Romney in 2006: “Romney calls Ronald Reagan his ‘hero’.”

All in all, this was one informative piece of foam rubber. And there were others highlighting Mr. Romney’s shifting positions on gun control, abortion, and gay rights.

But will the flip-flops bother the party’s base of conservative activists? Odd dynamics often seize a political campaign, crucial moments when a candidate sees a manageable difficulty spiral into a crisis.

Mr. Romney, who is trying to pump up his single-digit standing in opinion polls by appealing to social conservatives, has made himself vulnerable in one of the more dangerous of these moments — when doubts about a candidate’s political philosophy, which can often be debated and eventually overcome, become doubts about the candidate’s character, which usually can’t.

Several conservative activists I talked with at the conference cited Mr. Romney’s vote for Mr. Tsongas in the 1992 Massachusetts presidential primary. Yet, they were less disturbed by the vote itself than by Mr. Romney’s more recent explanation of it.

“In Massachusetts, if you register as an Independent, you can vote in either the Republican or Democratic primary,” Mr. Romney told ABC interviewer George Stephanopoulos last month.

“When there was no real contest in the Republican primary, I’d vote in the Democrat party for the person who I thought would be the weakest opponent for Republicans.”

Something here is too clever — either Mr. Romney’s original idea of casting his vote strategically, or his ex-post facto fashioning of an excuse for how he came to vote for Mr. Tsongas, who was not, incidentally, the weakest candidate in the Democratic field in 1992.

The general impression of excessive cleverness probably isn’t helped by Mr. Romney’s astonishing resemblance to Bob Barker, venerable host of “The Price is Right,” who shares the same chiseled jaw line and finely polished hair.

The game-show demeanor is on full display in a YouTube clip of Mr. Romney’s 1994 debate with Mr. Kennedy that has spread with viral momentum to the email inboxes of Republican activists. Again the problem wasn’t simply the views on social issues that Mr. Romney expressed — which are opposite to those he now holds — but also the evidently passionate, over-rehearsed sincerity with which he expressed them.

“You’re not going to see me waver on that,” he says on the 1994 clip after pledging his undying support for Roe v. Wade.

Now that he’s wavered into favoring the repeal of Roe, a large number of the CPAC activists were happy to cheer him when he spoke to them last Friday afternoon. An overflow crowd gathered around closed-circuit TVs spaced throughout the Omni Shoreham Hotel to see him deliver a speech packed with conservative rhetoric.

It was, needless to say, flawlessly delivered. It was also laced with subtle digs at his rivals for the nomination.

Mr. Romney took the podium with his wife, Ann, “my sweetheart,” as he insisted on calling her, to whom he’s been married for 37 years and whom he now brandishes like a merit badge — something the activists were unlikely to see from other Republican candidates, such as the thrice-married Rudolph Giuliani and Newt Gingrich.

Mr. Romney pledged to work to repeal the campaign finance legislation called McCain-Feingold — emphasis on Mr. McCain. And he blasted the immigration-reform bill known as McCain-Kennedy — emphasis on Mr. McCain again, but on Mr. Kennedy too.

Mr. Romney made many pledges, in fact. He noted he was the first 2008 presidential candidate to sign a pledge never to raise taxes. He pledged that as president he would hold nondefense discretionary spending to the rate of inflation “minus 1 percent.” He pledged to veto any budget that exceeded the cap.

He didn’t pledge “never to waver” on that pledge — and evidently he didn’t need to. On Saturday it was announced that Mr. Romney won the straw poll of the more than 1,700 CPAC registrants by a solid margin — 21% over runner-up Mr. Giuliani’s 17%.

Among the conservative activists, the anti-flip-flopper flip-flops flopped — at least for now.

Mr. Ferguson is a columnist for Bloomberg News.