Updated

Rep. Rodney Alexander (search) switched his party affiliation to Republican on Friday — making the surprise flip in the last minute of registration for the Nov. 2 ballot, virtually assuring the seat for the GOP.

Alexander, who ran as a Democrat to win his first congressional term but voted along conservative lines, had remained a Democrat Wednesday when he registered at the start of qualifying. At the time he said, "I'm not ashamed to be a Democrat, but I vote what I think the people of the 5th District want me to represent."

Alexander said Friday he had been struggling with his conservative votes for two years — backing the Bush tax cuts as well as the war in Iraq — and noted they had brought him criticism from Democrats.

"I just decided it would be best for me to switch parties, that I would be more effective in the 5th District in the state of Louisiana as a Republican," he said.

In Washington, Democrats reacted angrily.

"Rodney Alexander has betrayed voters in Louisiana and leaders like (Senators) John Breaux and Mary Landrieu (search), who have helped him. We have no use for turncoats like Rodney Alexander in the new Democratic majority," said Kori Bernards, spokeswoman for the Democratic Congressional Campaign Committee.

Alexander's decision leaves House Republicans with 229 seats to 205 for the Democrats with one Democratic-leaning independent. With the switch, Democrats must now gain 12 seats this fall to win the majority.

There is another strong Republican in the three-candidate field: Jock Scott, a former state representative from Alexandria. The remaining Democrat is Zelma "Tisa" Blakes, of Monroe, a political newcomer who called herself a "domestic engineer" when she qualified on Wednesday.

Asked if the party will get behind a political unknown, state Democratic Party chairman Mike Skinner said officials will explore all possible options.

Under the unique Louisiana open primary system, all candidates run on the same ballot regardless of party. If no one gets more than half the vote on Nov. 2, a runoff will be held in December.

Breaux, called Alexander's switch an underhanded maneuver that "effectively prevented the people of his district from a having a choice."

"Rodney is a confused politician who has placed loyalty at the very bottom of his priorities," Breaux said.

Rep. David Vitter, a Republican who is running for the retiring Breaux's seat, immediately endorsed Alexander.

"Rodney is someone who has stood up for conservative principles and Louisiana values. Unfortunately, the Washington Democratic leadership does not share these values," Vitter said.

There have been growing signs of Alexander's disaffection with his party, and in March he found himself under such intense pressure that he had to publicly announce he would remain a Democrat. Yet he skipped the party's National Convention last month in Boston.

Alexander acknowledged he had been courted by the Republicans but said President Bush (search) had not asked him personally to make the switch.

White House spokesman Scott McClellan said Bush called Alexander on Friday evening to welcome him to the party and wish him well.