Artur Davis, who backed Obama in 2008, to speak at GOP convention

This is Artur Davis’s job now, the work that he hopes will resurrect his political career. Wear a suit. Speak to strangers. Explain that what had been some of the most important causes of his life — a political party and a president — turned out to be mistakes.

“How many of us believed, four years ago, that Barack Obama was not just a politician?” Davis, a former four-term congressman, asked Mitt Romney supporters in Arlington County’s Ballston neighborhood on Wednesday. The Romney people said nothing, but Davis kept on: This was his story, not theirs.

“We may not have the power to stop it,” Davis said of President Obama’s campaign. “But the American people have the power to punish it.”

Four years ago, Davis was onstage at the Democratic convention: a fast-rising congressman from Alabama, so close to Obama that he provided the official “second” for Obama’s nomination.

On Thursday, the Republican Party said he would be a “headliner” at its convention in Tampa, where he will be one of Obama’s most prominent African American critics.

In between those two big convention moments, Davis was bounced out of politics after a disastrous attempt to mimic the Obama playbook in a run to become governor of Alabama. After the loss, he abandoned the Democratic Party, saying it had drifted too far left.

Davis’s new life reveals the benefits and burdens that come with being a celebrity turncoat.

“You have a converted sinner who’s standing in front of you right now, and I thank you for letting me stand here,” Davis told a tea party audience in Falls Church in July. At the front of that room, Davis seemed to marvel at his rapid success as an ex-Democrat.

“I used to go to the Baptist church in Birmingham,” he said. “And Baptists are good folks, but they won’t let nobody preach on week one, or month one, like y’all will.”

Even before Thursday’s news, the 44-year-old Davis (whose first name is pronounced “Ar-TOOR”) had already made a remarkable leap out of his political grave.

He has been out of Congress since early 2011. He left Alabama and moved with his wife into a new high-rise in Pentagon City.

Davis said he moved to Virginia to join a D.C. law firm, not to run for office. But last year, he called Democratic campaign consultant Mo Elleithee.

“I remember him specifically saying, ‘I still have the political bug. And I’m thinking about running in Virginia,’ ” Elleithee recalled Thursday.

Elleithee gave him bad news: running for Congress in Northern Virginia would mean taking on entrenched Democrats such as James P. Moran Jr. and Gerald E. Connolly. Davis, as a newcomer, would stand little chance.

Davis says he was just surveying the landscape in his new state: “I’m still not in a decision-making mode when it comes to running for office.”

A few months later, on May 29, Davis typed words that would change his life.

“If I were to leave the sidelines, it would be as a member of the Republican Party,” Davis wrote on his blog. “Wearing a Democratic label no longer matches what I know about my country and its possibilities.”