A small margin in votes separating incumbent Democratic Sen. Bob Casey from Republican challenger David McCormick Jr. has triggered a recount in the Pennsylvania Senate race, the commonwealth's secretary said Wednesday.

Despite the recount being called, it remains an uphill battle for Casey, who still trailed by more than 25,000 votes as of Thursday afternoon. He would need overwhelming success both in ensuring remaining ballots are counted, and that those voters picked him.

The unofficial results in the race for the U.S. Senate seat in Pennsylvania have triggered a legally required statewide recount, Commonwealth Secretary Al Schmidt said on Wednesday. Democratic Senator Bob Casey and Republican Dave McCormick have vote totals within the one-half of 1 percent margin that triggers a mandatory recount under state law,