In a move that all but assures Mitt Romney will become the GOP nominee for president, fellow candidate Rick Santorum decided Monday to drop out of the race.

Sources say Santorum called Romney to let him know before making the announcement at a press conference in Gettysburg, PA around 2 p.m. ET. The news came shortly after Santorum said he was resuming his campaign after a brief suspension when his daughter, Bella, was hospitalized due to complications from a rare genetic disorder.

The former Pennsylvania senator had been Romney’s top opponent, but suffered recent defeats in Wisconsin, Maryland and the District of Columbia, and recent polling in Santorum’s home state, which holds its primary on April 24, showed the numbers there had turned against him, as well. The Santorum campaign had previously called Pennsylvania a “must-win,” so it’s possible his withdrawal from the race was an effort to avoid an embarrassing loss on his own home turf.

Aside from Romney, only two GOP candidates remain — former House Speaker Newt Gingrich and Texas Rep. Ron Paul — but neither has shown the ability to overtake him in the race.

Watch part of Santorum’s announcement below.

[The Washington Post]