Pennsylvania’s Tom Corbett:

Pennsylvania GOP Gov. Tom Corbett has been in trouble all year, and a new poll out Tuesday suggests he’s trailing even the unknown Democratic candidates by double digits.

The poll, from the Democratic firm Public Policy Polling, finds Corbett behind his potential Democratic challengers by anywhere from 12 to 20 percentage points.

He trails both state Treasurer Rob McCord and former state Environmental Protection Secretary John Hanger by 19 points, both Rep. Allyson Schwartz and former state Environmental Protection Director Katie McGinty by 15 points and both Allentown Mayor Ed Pawlowski and businessman Tom Wolf by 12 points. He also trails former state Auditor General Jack Wagner, who hasn’t entered the race but is considering a bid, by 20 points.

Corbett’s approval ratings have also taken a further hit, per the poll: Just 24 percent of those surveyed approve of his job performance, compared with 65 percent who disapprove. PPP’s previous poll had his approval rating at 33 percent, with a 58 percent disapproval rating.

Corbett has been viewed as arguably the most vulnerable incumbent governor in 2014 and tops national Democrats’ list of targets for next year. Observers say his unpopularity in the state is a big part of why he’s drawn such a big field of Democratic challengers.

In the Democratic race, PPP finds Schwartz leading the pack with 21 percent, followed by Wagner at 17 percent, McCord at 10 percent, McGinty at 9 percent, Hanger at 8 percent and the other candidates at 4 percent or less. More than a quarter of Democratic primary voters, 27 percent, said they’re undecided.

This is hardly surprising. Corbett has been performing badly in polling for much of 2013, and there’s even been talk, which seems to have been aborted, of Keystone State Republicans replacing him on the ticket.  Corbett isn’t the only vulnerable Republican Governor, of course. Florida’s Rick Scott, Michigan’s Rick Snyder, and Maine’s Paul LePage all seem to qualify as vulnerable as well, although they are all polling far better than Corbett is at the moment. Obviously, numbers can change as time goes on but Corbett has a pretty big hole to dig himself out of even if 2014 turns out to be a good year or the GOP. However, at some point Corbett will find himself in a hole that may be impossible to get out of.