After his win in Wisconsin on Tuesday, Mitt Romney now holds a small five point lead over Rick Santorum in Santorum’s home state of Pennsylvania according to Public Policy Polling.

Mitt Romney’s taken the lead in PPP’s newest poll of Rick Santorum’s home state of Pennsylvania. Romney has 42% to 37% for Santorum with Ron Paul at 9% and Newt Gingrich at 6%. The numbers represent a dramatic turnaround from when PPP polled the state a month ago. Romney’s gained 17 points, going from 25% to 42%. Meanwhile Santorum’s dropped 6 points from 43% to 37%, for an overall swing of 23 points in the last four weeks.

Pennsylvania Republicans are expressing major doubts about Santorum’s viability both in the primary and the general election. Only 36% of GOP voters think Santorum has a realistic chance at the nomination to 54% who believe he does not. And when it comes to matching up against Barack Obama in the fall only 24% of Republicans think Santorum would provide their best chance for a victory while 49% think that designation belongs to Romney.

A loss in his home state would be the final nail in the coffin of the Santorum campaign, which already has basically no legitimate path to winning the nomination. More importantly, it would be a humiliating defeat for Santorum. Santorum has made Pennsylvania a must win and his firewall.

By doing surprisingly well this whole primary season, Santorum has significantly raised his profile and brand value with the conservative base. Santorum has good reason to not want to undo that by continuing a hopeless campaign seen as only damaging the Republican Party.

If more polls show Santorum losing Pennsylvania, I won’t be surprised if his campaign ended in the next few weeks, either before the Pennsylvania or soon afterwards.