Former Rep. J.D. Hayworth has been hinting for months that he will challenge John McCain in a Senate primary in Arizona next year. He gave the strongest hint yet on his radio show yesterday:

On his KFYI radio show Monday, Hayworth told his listeners that he went to Washington, D.C., this month and “we may have moved past due diligence into something that is more than a legal term of art . . . something called ‘testing the waters.’ So stay tuned on that.”

Federal Election Commission regulations allow candidates to set up preliminary “testing-the-waters” or “exploratory” committees without registering. But Hayworth would have to file an official statement with the FEC once he decides to become a candidate and spends or raises more than $5,000.

The primary election in Arizona is not until August 24, 2010, so there’s at least some time left for Hayworth to join the race. A Rasmussen poll from last month found McCain and Hayworth in a virtual tie, with McCain getting 45% to Hayworth’s 43%.

However, McCain has close to $20 million dollars left from his 2008 Presidential run, and could blanket the state with money during a primary, especially since the general election is not likely to feature a major Democratic challenger. In addition, McCain’s high-profile role during the health care debate may have solidified his standing among conservatives and the GOP base.

With the nation in an anti-incumbent mood, practically nobody in Washington is truly safe. But Hayworth was in Washington as recently as 2006, and he has his own corruption investigations from the Abramoff scandal to navigate, too.