Pennsylvania Gov. Tom Wolf is halfway through his first term and looking ahead to another run in 2018.

But a recent analysis by Governing Magazine has labeled the Democrat one the country's 12 "most vulnerable" governors.

There are several reasons for that.

One, Wolf's approval ratings are below 45 percent. 

Two, the governor is staring down a potential budget deficit in the current fiscal year of more than $500 million, and a shortfall in the coming budget year of as much as $1.7 billion.

Three, a number of heavyweight Republicans are considering a run, including House Speaker Mike Turzai, Senate Majority Leader Jake Corman, and U.S. Reps. Patrick Meehan and Mike Kelly. Scott Wagner, a state senator from York County who owns a waste collection business, has said he is kicking off his gubernatorial campaign next week. 

The fourth reason is a bit of a wild card.

"In 2018, we have the midterm election. That will be turned into a referendum on the new president, Donald J. Trump," said Franklin and Marshall College pollster and political scientist Terry Madonna.

"If President-elect Trump is successful and his job performance is high, that's going to definitely benefit Republicans," he said. "If not, if he's in trouble and Republicans are in trouble because of it, that would obviously help Gov. Wolf in his efforts."

Madonna said local issues, including how Wolf handles the state's looming fiscal challenges, will likely carry more weight on whether he wins re-election. But he said the effect of the national mood could not be ruled out. 

While unseating an incumbent governor is rare in Pennsylvania, it's happened recently. Wolf beat out one-term Republican Gov. Tom Corbett two years ago.