He spoke at the Democratic convention, endorsing Barack Obama for president.
"The last time I spoke at a convention, it turned out I was in the wrong place," said former U.S. congressman Artur Davis, a former Democrat who switched parties this year.
"What a difference four years makes," he added.
Davis -- who is now one of the Republican Party's most prominent African Americans -- served four terms in the U.S. House before entering the Alabama governor's race in 2010; he lost in the Democratic primary.
Saying tonight that Republican nominee Mitt Romney "knows how to lead" the nation out of its economic problems, Davis added that "America is a land of second chances. And I gather in this close race you have room for the estimated 6 million of us who got it wrong in 2008 and want to fix it."
As for others who voted for Obama in 2008, Davis said: "Ask yourself if these Democrats still speak for you."
Davis scorned Obama for high unemployment and negative campaigning, saying his administration is more about glitz than governing.
"May it be said of this time in our history: 2008 to 2011, lesson learned," Davis said. "2012: mistake corrected."
Many Democrats have criticized Davis' party switch. Hours before the convention speech, Davis' former colleagues with the Congressional Black Caucus wrote an open letter that accused him of sheer opportunism.
Noting that Davis has reversed all his former positions, 14 CBC members wrote: "We have come to the disturbing conclusion that your recent public statements have no basis in real policy or political disagreements, but rather they stem from transparent opportunism and a personal determination to overcome failing to win the Alabama Democratic primary for Governor in 2010."
