SENATOR, YOU’RE ONE OF THEM…. We’re well past the point at which it’s reasonable to ask, “What happened to John McCain?” Nevertheless, the Arizona senator’s latest campaign ad is yet another reminder of just how little integrity McCain has left.

In the spot, viewers see McCain chatting with an Arizona sheriff — who has worked with Joe Arpaio — who’s complaining about “illegals in America.” The senator chats with him about a proposed solution, with McCain concluding it’s time to “complete the danged fence.” The sheriff adds, “Senator, you’re one of us.”

It’s not altogether clear who counts as “us.”

Possible subtexts notwithstanding, the ad is laughable for anyone who’s been following McCain’s work on immigration policy. While his new message emphasizes the need to “complete the danged fence,” the senator has consistently taken the exact opposite position. He’s voted against funding for building a border fence; he’s dismissed the same plan he touts in the ad as being little more than “public relations”; and he’s even been quite candid about why a fence wouldn’t be effective.

But that was before McCain feared losing support from his far-right base in the midst of a primary challenge. Indeed, if his new ad tells voters anything, it’s that McCain is genuinely worried about his re-election prospects. Despite having universal name recognition, the power of incumbency, and an enormous edge on fundraising, McCain wouldn’t bother with a ridiculous ad like this one unless he seriously thought he might lose to a right-wing radio personality in the GOP primary.

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.