Public Policy Polling, the Democratic firm that nailed Barack Obama’s narrow Indiana and North Carolina wins in 2008, says he’s showing considerable vulnerability in Pennsylvania, where Mitt Romney has pulled even at 44 percent to 44 percent, and wins 18 percent of Democrats:

Pennsylvania is looking more and more like it could be a tough hold for Barack Obama in 2012. His approval rating in the state continues to be under water at 46/48. More voters have expressed disapproval than happiness with Obama on all three polls PPP has done in the state so far in 2011. And even though Obama took Pennsylvania by 10 points in 2008 the best he can muster right now in a head to head match up with Mitt Romney is a tie.

While PPP ascribes Obama’s issues there to losing so-called “Hillary Democrats” — the lower-middle class white voters we heard so much about during the primary — the real difference between Pennsylvania, where Obama won by double digits last time, and tougher states he barely won in 2008 where he now actually has better numbers, like Ohio and Florida, is the governor.

Tom Corbett, the Republican elected governor of Pennsylvania on last fall’s Tea Party wave, is no moderate, but he’s not making headlines for trashing unions and cutting essential services the way Rick Scott in Florida and John Kasich in Ohio are. These extremely unpopular Republicans are already a drag on their party’s efforts to recapture the White House, and they’ve only had half a year in office.