The reasons are obvious, the News 12 anchor says.

The Supes will appoint a successor who will undue everything Arpaio has done and make his life miserable… and he might not win the general, even if he mops up the primary:

But Arpaio’s vaunted poll numbers slipped as the investigations of his office came to light. He has provided a wealth of negative headlines and sound bites that would be joyfully exploited by the likely Democratic nominee Terry Goddard.

He would appear to many voters as a candidate with no real interest in running the governor’s office (“the governor gets other people to do those things,” he said Friday). Who would those “other people” be?

In a debate he would appear out of touch and, perhaps, at 77, not up to the job.

Meanwhile, the PBJ, citing sources, says Arpaio will announce he’s not running today:

Maricopa County Sheriff Joe Arpaio will announce this afternoon he is not running for governor this year, sources say.

Arpaio has been contemplating a run in the Republican primary for some time, but four sources familiar with the decision say the controversial sheriff will not run. An official announcement is expected this afternoon.

The Business Journal story goes out of its way to note that ABC-15 reported last week that the sheriff would run.

More: Greg Sargent’s WashPost Plum Line blog says the same thing:

But a source close to Arpaio, a leading advocate of the law who’s despised by immigrants’ rights groups, essentially told me just now that he’s not going to do it.

I’m told that Arpaio, the Sheriff of Maricopa County, will not be holding a press conference today, and will only be issuing a one-page statement at 4 P.M. eastern time explaining his decision. Asked if this meant he isn’t running, a source close to him said: “That would be a smart reading of the game plan here.”