Former Sen. Rick Santorum, R-Penn., will drop out of the U.S. presidential race, effectively leaving the endorsement to Republican frontrunner Mitt Romney. Santorum will make the announcement Tuesday afternoon at a news conference in Gettysburg, Penn., according to the Washington Post.

Last week, Romney defeated Santorum in Wisconsin, Maryland and the District of Columbia.

Santorum argued that likely Republican frontrunner Mitt Romney isn’t conservative enough to beat Pres. Barack Obama at the polls in November. Santorum spent the weekend with his daughter, who was hospitalized with pneumonia.

Former Speaker of the House Newt Gingrich and Texas Rep. Ron Paul are still in the race, but Romney leads them in delegates.

For Republican candidates' delegate counts, click here.