An automatic recount has been triggered in the U.S. Senate race in Pennsylvania between Bob Casey and Dave McCormick. Here's how the recount will work.

Republican Dave McCormick leads Democratic Sen. Bob Casey by about 28,000 votes, under the 0.5 percentage point threshold for an automatic recount under state law.

The Pennsylvania Senate race between incumbent Bob Casey, left, and his Republican challenger, Dave McCormick, is headed for a recount. All counties must complete their recounts by Tuesday, Nov. 26. Pennsylvania's Senate race is going to a mandatory recount despite the Associated Press calling it last week for Republican challenger Dave McCormick.

The U.S. Senate election in Pennsylvania between Democratic incumbent Sen. Bob Casey and Republican David McCormick is headed for a statewide recount, as counties continued Wednesday to sort through outstanding ballots and the campaigns jousted over which ones should count.

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.

The U.S. Senate race in Pennsylvania will now go to a recount, Secretary of the Commonwealth Al Schmidt has announced.

Unofficial results for the US Senate seat in Pennsylvania have triggered a legally required statewide recount of the race, which the Associated Press last week called for Republican David McCormick, a former hedge fund CEO.