[cnn-photo-caption image= http://i2.cdn.turner.com/cnn/2010/images/07/14/art.mccain0330g.gi.jpg caption ="A new poll shows Sen. John McCain has a strong lead in the Arizona Republican primary race."]
(CNN) - Sen. John McCain is widely ahead of his two primary challengers, according to a new poll.
A Behavior Research Center survey released Thursday indicates that 64 percent of likely Arizona Republican primary voters support McCain, with19 percent backing former Rep. J.D. Hayworth, five percent supporting Jim Deakin, a Tea Party activist, and 12 percent undecided. The primary is scheduled for August 24.
McCain, the GOP's 2008 presidential nominee, is bidding for a fifth term in the Senate.
The poll was conducted June 30-July 11, after media reports that Hayworth appeared in a 2007 infomercial that promised billions of dollars in free government grants. The McCain campaign subsequently launched two television ads that targeted Hayworth's past ties to the company that aired infomercials. The company – National Grants Conferences – has been criticized by the attorneys general of multiple states for deceptive marketing and has an "F" rating from the Southeast Florida and Caribbean Better Business Bureau.
McCain led Hayworth 54 to 28 percent in their previous poll, conducted in April.
Earl de Berge, Behavior Research Center's research director, says that McCain has hurt Hayworth "on ethics issues pertaining to being a lobbyist and so on. Most Republicans just pinch their nose at that stuff, and I think it just turned them off to him. It's the devil you know versus the devil you don't know."
The McCain campaign is pushing out on its email distribution list an Arizona Republic report on the new poll. CNN reached out to the Hayworth campaign for reaction, but the campaign has yet to respond.
The Behavior Research Center poll was conducted June 30-July 11, with 524 registered voters questioned by telephone. The survey's overall sampling error is plus or minus 4.4 percentage points and 6.5 percentage points for questions only to Republicans and independents likely to vote in the GOP primary.
Follow Paul Steinhauser on Twitter @psteinhausercnn