UPDATE: Rick Santorum announced the suspension of his presidential campaign during a 2 p.m. press conference on Tuesday. Santorum, who vowed that he is not done fighting, did not endorse Mitt Romney for president.

Santorum announced his withdrawal at a campaign event taking place in Gettysburg, Pa., the site of the pivotal Civil War battle, according to reports from ABC News and the Washington Post.

The former Pennsylvania senator emerged from a slow start to become one of the front-runners of the Republican primary, trailing the presumed nominee Mitt Romney by only a few percentage points in some regions.

Announcement Follows String Of Defeats

Santorum's announcement comes after he suffered a string of defeats in last week's Wisconsin, Maryland and Washington, D.C. primaries. The possibility of losing Pennsylvania in the state's GOP primary on April 24 may have also fueled the decision, as many political insiders speculated Santorum's hopes for a future political career would be dashed if he did not win his home state.

In addition, his young daughter, Bella, was hospitalized for the second time this campaign due to complications from the rare genetic disorder Trisomy 18, an event some speculate may have encouraged the candidate to pull out of the presidential race.

Former House speaker Newt Gingrich and Rep. Ron Paul, R-Texas, remain in the race, but neither candidate has demonstrated an ability to be a formidable alternative to Romney.

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