Allahpundit noted the likelihood of J.D. Hayworth’s primary challenge to John McCain last night, and today the AP makes it official … or officially non-official.  While emphasizing that he didn’t want to officially declare his candidacy — which would create a set of legal obligations that he’s not quite ready to assume — Hayworth quit his radio show on air and later stated his intention to challenge McCain:

Former Arizona Congressman J.D. Hayworth says he is planning to run against John McCain for his U.S. Senate seat.

Hayworth, a Republican, told The Associated Press late Friday he stepped down as host of his radio program on KFYI-AM, a conservative radio talk show in Phoenix. Legally, he would not have been able to remain host of the program and be an active candidate. …

“We will formally announce at a later time, but we’re moving forward to challenge John McCain,” he said. “I think we all respect John. I think his place in history is secure. But after close to a quarter-century in Washington, it’s time for him to come home.”

It’s not the first time that a former member of a major-party presidential ticket found himself challenged within his party for his existing Senate seat the next cycle.  The same thing  happened, ironically, to one of McCain’s closest friends in the upper chamber, Joe Lieberman.  Lieberman lost his primary to Ned Lamont, who mostly self-financed from his personal fortune.  Lieberman won the seat in the general election by running as an independent, but still caucuses with Democrats, even though Lieberman campaigned for McCain in 2008.

Hayworth doesn’t have a personal fortune like Lamont on which to run, but he’ll need the money.  According to the AP, McCain already has $5 million in the bank, and he’s already spending it against Hayworth on radio ads.  If Hayworth can tap into grassroots disaffection in Arizona as Scott Brown did in Massachusetts, the money gap may not be as significant as it normally would, but he’ll still need to raise money for organization and GOTV efforts.  His contribution levels will tell a story about his chances against McCain’s entrenched power in the state.

The biggest loser from this may well be Sarah Palin.  Under normal circumstances, grassroots activists would expect Palin to either stay out of the race or support the more conservative, grass-roots candidate against the entrenched Republican establishment.  Michelle has written an excellent column detailing the pitfalls of intervening in a primary fight for Palin, and one has to wonder why she felt the need to do so, and why McCain asked for her help.  Her cachet comes entirely from positioning herself as an outsider, and now she’s rallying to the defense of one of Washington’s insiders.  If that was in the general election, everyone would hail that as an example of realpolitik, but in a primary, she’s going to get some valid criticism for this choice.

Hayworth will still be a long shot, but primaries are a hygienic device that keeps incumbents accountable for their performance.  In this case, the campaign promises to be a long one; the primary election will be held on August 24th.  That gives almost exactly seven months for Hayworth and McCain to make their cases to the voters of Arizona, and they will be the biggest beneficiaries of the process.