Recent polls have showed Pennsylvania Gov. Tom Corbett in a slump, which has prompted a spate of speculation about potential challenges against him in 2014. Nobody can remember the last time an incumbent governor here lost a re-election campaign, but you never know.

But I had to smile when I saw the item in PoliticsPa last week reporting that wealthy Philadelphia businessman Tom Knox was saying he would run against Corbett. Knox has said such things before, and backed out - in the 2010 governor's race and Philadelphia's 2011 mayor's race.

So he'll have a bit of a credibility problem selling anyone on the idea that he's really in it. But that matters less for Knox than others because his wealth can make him a credible candidate overnight. We'll see.  Knox really did run for mayor in 2007, finishing second to Michael Nutter in a crowded Democratic primary.

But for fun, PoliticsPA deputy editor Kelly Cernetich offers the long list of other potential Democratic candidates: former Allegheny County Executive Dan Onorato (he ran last time), Auditor General Jack Wagner (also ran last time), U.S. Sen Bob Casey (ran in 2002), State Treasurer Rob McCord (will definitely run some time), former U.S. Rep. Joe Sestak (lost to Pat Toomey for Senate), and U.S. Rep. Allyson Schwartz (huh? I said it's a long list). And he wasn't on this list, but Montgomery County Commissioner Josh Shapiro is another guy to watch.

A little history lesson

It's too early to say if Corbett will really be vulnerable in two years. There's plenty of history of incumbents polling poorly against generic opponents and then trouncing real ones.

And as we said, nobody remembers when a sitting Pennsylvania governor lost a re-election bid.

But a few of us remember when one almost did. It was 1982, and Republican Gov. Dick Thornburgh was running for re-election. A lot of powerful Democrats tried to talk Philadelphia's charismatic young District Attorney, a guy named Ed Rendell into running against Thornburgh.

Rendell declined and the Democratic nomination went  to Allen Ertel, a little-known congressman from Williamsport. The economy went into a tailspin and Ertel came within three points of knocking off Thornburgh.

Like I said, you never know.