2006 California's 50th congressional district special election

During the campaign, Arizona Senator John McCain cancelled a planned fundraiser for Bilbray at the last minute, after Bilbray criticized McCain's immigration bill as "amnesty" for illegal immigrants.[4] Later, McCain contributed money to Bilbray's campaign and voiced a radio commercial for the National Republican Congressional Committee in support of Bilbray's race against Busby.[5]

On June 2, five days before the special congressional election, Busby was recorded telling a largely Hispanic group that "You can all help--you don't need papers for voting, you don't need to be a registered voter to help." This comment was in response to a question by a man who asked in Spanish, "I want to help, but I don't have papers."[6] The recording was circulated over the Internet and on radio. Republicans claimed Busby was encouraging people to vote illegally, while Busby claimed she misspoke and meant that a person does not need to be a registered voter to help her campaign (such as phoning registered voters).[7]

A number of irregularities in the election were alleged, including the swearing in of Bilbray by a member of his own party 17 days before the election was certified, "electronic voting machines sent out to the homes and cars of volunteers for up to 12 days prior to the election, and irregular election results like huge mega-precincts of absentee ballots where turnout was thousands of percent more than registered voters." The Democratic National Committee's Voting Rights Institute raised several concerns about the fairness and accuracy of the vote count.[8] An election contest lawsuit sought a hand recount.[9] The court dismissed the suit on the basis that, once the House of Representatives had sworn in Bilbray, the court lacked jurisdiction to hear the challenge.[10]

Political analyst Larry Sabato wrote in his Crystal Ball newsletter: "What a difference four percentage points makes! That was Bilbray's margin over Busby, a gaffe-prone, lackluster candidate who was out of her league. With six years (1995–2001) under his belt from another California House district, former congressman Bilbray understood what it took to win a tough campaign, and riding the immigration issue, he did so. The DCCC forced the NRCC to pull out all the stops and spend a large fortune for Bilbray, but given the dam that might have burst had Busby won, it was worth every GOP penny for them."[11]