WASHINGTON – Mitt Romney is the godfather of what Republican critics call Obamacare. Newt Gingrich is an adulterer on his third marriage. Tim Pawlenty is too green — environmentally, that is.

Jon Huntsman worked for President Barack Obama. And Haley Barbour has come off as dismissive of racial segregation.

Is any potential Republican presidential nominee without vulnerabilities that could alienate voters, especially those in the GOP primaries, and provide ready-made attacks for opponents?

Not in this crop.

The 2012 Republican field is deeply flawed, lacking a serious GOP contender without a personal misstep or policy move that angers the party base. Each of those weighing bids has at least one issue that looms as an obstacle to White House ambitions, and that could derail the candidate if not handled with care.

That explains why the would-be candidates are trying to confront their troubles early on, just as the nomination fight gets under way. They’ll have to answer for black marks on their records — and insulate themselves from criticism — repeatedly between now and early next year when voters cast the first caucus ballot.

Their aides are trying to figure out how to weather the attacks likely to show up in mailings, online or in television ads; responses are likely to be included in media interviews, debate appearances and, perhaps, even in major speeches. Aides also are studying — and testing — the best ways to exploit their opponents’ weaknesses. Already, Internet sites like Facebook, Twitter and YouTube are magnifying their woes, and every embarrassing document, speech or utterance is certain to appear online.

Candidates can’t simply ignore their flaws or obstacles; their challengers certainly won’t.

Just ask Democrat John Kerry. He was vexed in 2004 by questions about his service in Vietnam and about his reputation as an elitist. Only after widely debunked claims about his Vietnam record started to sink his poll numbers did the campaign effectively respond — and by then it was too late.

“You really have to drive the boat into the fire and be fearless about your record,” said Michael Meehan, a Democratic consultant on Kerry’s campaign.

Romney, for one, has started to address his biggest policy problem: the health care plan he signed into law as Massachusetts governor, which Obama and the Democrats used as the basis for their national overhaul plan. The White House gleefully points out the similarities.

“Our experiment wasn’t perfect — some things worked, some didn’t, and some things I’d change,” Romney said recently in New Hampshire. But, he added, “one thing I would never do is to usurp the constitutional power of states with a one-size-fits-all federal takeover.”

Romney also will face a repeat of the 2008 criticism that he’s inauthentic, particularly after a series of reversals on gay rights and other social issues.

Gingrich’s two failed marriages are well-known; the circumstances around them may not be and present plenty of fodder for rivals.

The former House speaker sought a divorce from his first wife while she was undergoing cancer treatment. His second marriage ended with an admission of an extramarital affair as he was pursuing the impeachment of President Bill Clinton for lying about sexual encounters with a White House intern. He married that mistress, 23 years his junior. Callista Gingrich is prominently featured in his campaign, appearing with him at events and on his website.

He was widely mocked for this recent explanation about his infidelity: “There’s no question at times of my life, partially driven by how passionately I felt about this country, that I worked far too hard and things happened in my life that were not appropriate.”

It remains to be seen whether Republicans heed his plea and focus on the future. “If the primary concern of the American people is my past,” he has said, “my candidacy would be irrelevant.”

Barbour can’t deny his trifecta of issues that make some skeptical. So he owns them.

“Let me just make this very plain: I’m a lobbyist, a politician and a lawyer … and I am willing to have my record in front of everybody,” says the Mississippi governor, who was head of the Republican National Committee and the Republican Governors Association. He also founded a booming lobbying operation and was dubbed the King of K Street, a reference to the capital’s downtown lobbying corridor.

The governor of a Deep South state, Barbour opened himself up to criticism when he bungled questions about the Ku Klux Klan and segregation.

Huntsman, the former Utah governor, is taking heat for his job as Obama’s ambassador to China.

John H. Sununu, once chief of staff to President George H.W. Bush and ex-chairman of New Hampshire’s GOP, called Huntsman an “Obamaite” who would never earn the trust of primary voters.

Huntsman leaves his post in April and can’t say anything until then. But his advisers have a ready-made response: He served his country, not necessarily the Democratic administration.

Obama, for one, isn’t going to let him off that easily; he’s thanked Huntsman for being an “outstanding advocate for this administration and this country.”

Obama chief of staff Bill Daley lays on the praise: “He’s played an integral part in this administration’s foreign policy.”

Romney and Huntsman face another obstacle. Both are Mormons, a religion that evangelicals who have considerable sway in Iowa and South Carolina look at warily.

Pawlenty, who on Monday announced he had formed an exploratory committee, once backed climate change legislation that conservatives deride. Advisers to the former Minnesota governor know it will be a problem.

He’s reversed his position on the issue, but his past words are certain to come back to haunt him.

“So, come on, Congress. Let’s get moving,” Pawlenty says in a 2008 commercial for the Environmental Defense Action Fund that urges, “Cap greenhouse gas pollution now.”

It’s available online. So are details of climate change legislation he signed that would reduce greenhouse gas emissions by 15 percent by 2015.

Among others weighing bids:

_Former Pennsylvania Sen. Rick Santorum may be dogged by his dismissal by voters in the 2006 election.

_Ex-Gov. Mike Huckabee of Arkansas faces questions about commuting the sentence of Maurice Clemmons, who in 2009 opened fire in Tacoma, Wash., and left four police officers dead.

_GOP vice presidential nominee Sarah Palin’s unorthodox resignation in the middle of her first term as Alaska governor — as well as her reality show stints and her countless impolitic comments — will be certain fodder for opponents.