Jim Nixon, a retired Army officer and staunch conservative, has voted Republican in every presidential race since Dwight D. Eisenhower topped the ticket. But not this time. "I've been a lifetime Republican, but that's in the past. No more," Mr. Nixon said. Like a small but significant cluster of lifelong Republicans, the Tucson, Ariz., resident plans to make a statement by breaking with the Republican Party this year. The reason: He's furious over President Bush's proposal to grant resident status to illegal immigrants, known by critics as his amnesty program. Not that Mr. Nixon plans to vote for the Democratic...