Only about 3 to 5 percent of voters are truly undecided between Mitt Romney and Barack Obama. Focus groups run by Republicans have found that some of the most effective ads appealing to those voters feature Democrats and independents speaking candidly about how they voted for Obama in 2008 but are now disappointed.

That’s one of the reasons that Republicans have decided to showcase former Democratic congressman Artur Davis of Alabama as a “headline” speaker at their convention. Davis, a moderate black Democrat who voted against Obamacare in 2010 and was crushed later that year in a Democratic primary for governor, has since left the Democratic party and is backing Mitt Romney. He was an early Obama supporter — the first Democratic congressman outside Illinois to endorse the candidate in 2007. He seconded Obama’s nomination for president at the 2008 Denver convention.

“The Obama I endorsed was the constitutional-law professor who said he supported the rule of law,” Davis explained to me. “Instead, we got someone who always went to the left whenever he reached a fork in the road.” Now Davis spends a great deal of time describing his conversion to Republican audiences. Even Jamelle Bouie, a writer for the left-wing American Prospect who doesn’t find Davis’s conversion story all that compelling, acknowledges its power. “Davis, like Joe Lieberman before him (and Zell Miller before that), can tell a credible story of ideological alienation,” Bouie wrote in the Washington Post. “He thought the Democratic Party was a big tent, but now — under Barack Obama — it is a haven for intolerant leftism.”

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