U.S. Senator John McCain has endorsed Ben Quayle over David Schweikert in the Republican primary for Arizona's Sixth Congressional District. McCain endorsed Quayle, a House freshman and the son of former vice president Dan Quayle, in a press conference Wednesday in Phoenix. Dan Nowicki of the Arizona Republic reports:

At a late afternoon news conference in Phoenix, McCain held up a Schweikert campaign mail piece that says Quayle “goes both ways,” a common phrase to describe bisexuality. The other side of the mailer explains that the accusation is that Quayle goes both ways on conservative issues. “This is not appropriate,” McCain, R-Ariz., said as a solemn-faced Quayle and U.S. Sen. Jon Kyl, R-Ariz.. looked on. “This crosses the boundary of decent political dialogue and discourse. This is not something that is acceptable at all.” McCain also criticized Schweikert for voting against a defense bill.

Schweikert, who is also a freshman House member, claims to lead Quayle by 20 points according to an internal poll. Both candidates were forced to run against each other in a newly drawn district for the August 28 primary, and the race has gotten particularly nasty:

At the time he decided to run against Schweikert, Quayle actually lived just barely inside the (Democratic) Ninth, a few hundred yards from the district line. Quayle has since moved into the Sixth. Schweikert has called Quayle a “carpetbagger.” “Some of us live in the district, some of us don’t,” Schweikert said during a televised debate in July. “I mean, my whole life and infrastructure is in the district.” He gestured toward Quayle, sitting to his right. “His is not.” In May, the Quayle campaign even accused the Schweikert campaign of spying. As a Quayle spokesperson told the Daily Caller, a young woman came to the Quayle headquarters and asked to volunteer. A staffer tried to verify the young woman’s contact information and found she had listed as her home address a local Islamic community center. The staffer later stopped by the Schweikert headquarters and claimed to have found the would-be volunteer sitting at the front desk, along with 18 “Quayle for Congress” yard signs.