Newt Gingrich plans to formally leave the Republican presidential race next Tuesday, senior campaign aides told Fox News, after struggling for months to turn around his sagging bid for the White House.

The former House speaker will "more than likely" endorse Mitt Romney when he makes his announcement to either suspend or end the campaign, a source said.

The decision comes after Gingrich huddled with senior advisers following the five primaries Romney swept on Tuesday night. Romney's victories made it virtually impossible for Gingrich to secure the 1,144 delegates needed for the Republican nomination...