Trump had a brief run for the Republican presidential nomination, but backed out before the first debate. He has also flirted with running on a third party ticket.
Early reports suggested that Trump would endorse former House Speaker, Newt Gingrich. Gingrich was one of the few candidates that accepted an invitation to a Trump moderated debate, which fell through after too few candidates agreed to come. Romney refused to attend the Trump debate.
Update: Donald Trump has officially endorsed former Massachusetts Gov. Mitt Romney for president.