Republicans on Wednesday were celebrating the defection to the GOP this week of a former Democratic congressman and close ally of President Barack Obama, saying that it underscored their argument that the president has led the country on a march to the left.

Former Alabama congressman Artur Davis, once a rising star in the Democratic Party and the man who helped put Obama’s name in nomination for the presidency in 2008, announced his intention to switch parties and said that he will vote for Mitt Romney in November.

“The fact that he has the courage to analyze the problems with the current administration on the issues of unifying diverse interests in America and creating jobs tells me this is a guy with a lot of principle,” said Virginia Gov. Robert McDonnell, R, who said he plans to call Davis in the next few days to welcome him to the party.

Davis, a centrist who opposed the Democratic health-care bill, said he may run for elected office as a Republican in Virginia.

Republicans saw in Davis’s announcement potent confirmation of their charge that Obama has failed to spark economic growth or deliver on his promises of fostering more national unity, both central planks of Davis’s critique.

In Virginia, Republicans saw in the black Harvard graduate an appealing potential candidate who could shake up the growing Democratic sway in northern Virginia.

“All I can say his analysis of the problems facing America are spot-on and his credentials are impeccable,” said McDonnell. “That’s a great start for being a candidate in northern Virginia or anywhere else in the Commonwealth of Virginia.”

Davis’s drift from the Democratic Party had been building for years, and Democrats dismissed his desertion as a tactical shift by a politician with wounded ambitions: Davis left Congress after he ran for governor of Alabama two years ago but failed to win his party’s nomination for the job.

But Davis’s political profile, his past vocal support of Obama and his pointed critique of the Democratic Party do create an opening for the GOP. Davis was the first congressman outside the president ‘s home state of Illinois to endorse Obama in 2007.

In an interview, Davis said he believes there is little tolerance in Democratic politics for “center-right” views like his own.

“The conventional wisdom in this town is that the Democrats have stayed in one happily tolerant place and that Republicans have moved to the hard right,” Davis said. “I can assure you that in the Democratic Party, there is substantial intolerance for people who deviate from the party line.”

As an example, Davis cited widespread criticism from the left of Newark Mayor Cory Booker, who apologized last week after saying on “Meet the Press” that he disagreed with attacks by the Obama campaign on Republican presidential candidate Mitt Romney’s record as a former executive at private-equity firm Bain Capital.

“The timing of that was purely coincidental,” Davis said. “But it certainly was exhibit number 32 of the point I’m making.”

Davis’s move came as the ranks of moderate Blue Dog Democrats in Congress have been thinning because of member retirements and electoral defeats at the hands of candidates on both the left and right.

It also came as Republicans have been working to highlight and promote black GOP lawmakers: There are two black Republicans serving in the House, and the GOP feels good about its chances of electing its first black woman, Mia Love of Utah, in November.

Davis was a vocal opponent of the Democratic health-care bill — the only member of the Congressional Black Caucus to vote against it. In a statement, he decried what he described as the Democratic embrace of identity politics and said he he believed the nation’s lack of economic growth was a larger problem than the “exaggerated inequality” Democrats have emphasized.

Davis also criticized Obama for failing to unite the country as he promised.

“When you run for office and the main qualification you offer is that you can break stalemate and gridlock, and it doesn’t happen and it gets worse, I think you have you be judged by that standard,” he said in an interview.

A spokesman for the Obama campaign declined to comment. But Rep. Gerald Connolly, D-Va., whom Davis confirmed he might challenge in 2014, said voters widely understand that Obama has been confronted with a “mindless, implacable” opposition of a Republican Party unwilling to ever compromise.

“I think Mr. Davis, in his bitter disappointment with the response to his ambition in his own party, is looking for a scapegoat. And I think he’s looking in the wrong direction,” Connolly said. “I think it says a lot about Mr. Davis. I don’t think it says anything about President Obama.”

An Alabama native, Davis said he has lived mainly in Virginia since late December 2010. He served 10 years in Congress. In 2010, he unsuccessfully sought the Democratic nomination for Alabama governor, emphasizing his willingness to challenge party leaders, but he lost the primary 62 percent to 38 percent to agriculture commissioner Ron Sparks, who went on to lose to the Republican nominee.

Davis lives in Pentagon City but said he’s had conversations with Virginia Republicans about running for Congress in 2014 or 2016 from a variety of seats — or seeking election to the Virginia General Assembly in 2015.

He said he may also choose never to run for elected office again. If ambition were the true motivation behind his public statement, he said, he’d have announced a run as a Republican in Alabama, where the party is dominant, instead of in hotly contested Virginia.

Other moderate Democrats said that Davis is unlikely to find a more receptive home in the Republican Party and could struggle to win support in Virginia’s conservative GOP.

In a lengthy statement explaining his party switch, Davis noted that he disagrees with the GOP’s hard-line stance on immigration and its resistance to closing some tax loopholes.

“I don’t believe, based on what I’ve seen with regard to the tea party and the Republican Party, that they are any more accommodating to centrists than the Democratic Party is,” said Rep. Jason Altmire of Pennsylvania, a moderate Democrat defeated in a party primary in April by a more liberal candidate.

But Altmire added that both parties need to engage in self-reflection about better reflecting centrist views.

“At the electoral level, there are people who are trying to purge the moderates — both from the left and right,” he said. “I think there needs to be some soul searching.”

Rep. Jesse Jackson Jr., D-Ill., said he sympathized with Davis’s diagnosis of the problem but was puzzled by his solutions.

“I, too, have a lot of reservations and criticisms of the current Democratic Party . . . but the Democratic Party comes a whole lot closer to my views than the current Republican Party, which I see as dominated by an extremist conservative ideology rooted in the past,” he said.

But McDonnell said the Virginia party is a big tent where Davis will be welcome.

“It’s the Reagan test,” he said. “If you agree with me 80 percent of the time, you’re my friend.”