That decision pits the two colleagues against each other in what is expected to be a bloody primary.

"Like most family disputes, I'm pretty confident it will end up in the middle of the street somewhere," said Chuck Coughlin, a Republican strategist in Arizona.

Schweikert's campaign said he would do what was necessary to win the primary, adding that internal polling suggested he was making gains among voters in the part of the district he didn't previously represent.

"We're disappointed, as I'm sure most Republicans are, that he decided to carpetbag over to our district," said Schweikert spokesman Chris Baker. "My sense is that Quayle's going to have to go negative to have a chance of winning. I don't think at this point that we do."

Quayle has proven himself a formidable primary candidate, though, defeating five other Republicans in a hard-fought primary in 2010.