Touting himself as an anti-abortion, pro-gun centrist Democrat, Melancon said in his written announcement Thursday that he is running against Vitter because Louisiana needs a more bipartisan approach in the Senate.
Melancon, the only Democratic member of Louisiana's House delegation, is in his third two-year term in the House. He is a former state legislator and a businessman whose resume includes a stint as president and general manager of the American Sugar Cane League, which lobbies on behalf of sugar cane farmers and processors.
Vitter, also a former member of the Louisiana Legislature, is an attorney. He succeeded Rep. Bob Livingston in the House and moved on to the Senate in 2004. He was the state's first Republican senator since Reconstruction, having won on a platform stressing his conservatism on fiscal and social issues.
He looked vulnerable after news broke in 2007 that his phone number was among the records of a Washington prostitution ring. Admitting only to an unspecified "serious sin," Vitter refused to answer questions about the scandal and has denied other allegations of involvement with prostitutes.
Vitter kept a low profile for months but emerged last year as a vocal critic of government bailouts of troubled businesses and, later, as a strong opponent of Obama's fiscal stimulus package and health care proposals - popular stances in a state that went strongly for Sen. John McCain in the 2008 presidential race.
Melancon does not mention the scandal in his announcement or an accompanying video.
"I'm announcing my candidacy for the US Senate to replace David Vitter because Louisiana deserves better," he says in the video. "Louisiana needs a different approach. More bipartisan. More disciplined. More honest and with a whole lot more common sense."
Campaign spokesman Bradley Beychok said in a recent interview that the scandal is bound to come up. "David Vitter has a long history of not practicing what he preaches and whatever opponent emerges is going to play that out in a lot of ways," Beychok said.
Still unclear is whether any other well-known candidates will enter the race.
Louisiana Secretary of State Jay Dardenne and recently retired state Supreme Court Justice Chet Traylor have acknowledged interest in entering the Republican primary next year but have not committed. An adult movie star from Louisiana, Stormy Daniels, created a stir when she said she might enter the race. She later made four stops on a "listening tour" of the state and formed an exploratory committee but has not yet declared her candidacy.
Neither Vitter nor his spokesman was immediately available for comment but the Republican Senatorial Campaign Committee wasted no time reacting to the announcement, issuing a statement casting Melancon as a liberal who votes "hand in hand with Speaker Pelosi."