Former rival Ben Carson backed Republican presidential front-runner Donald Trump on Friday, becoming the second former presidential candidate to support the billionaire businessman in the race for the White House.

Carson, a retired neurosurgeon who dropped out of the race on March 4, follows New Jersey Governor Chris Christie, a former candidate who also backed Trump after earlier dropping out of the race for the party’s nomination ahead of the Nov. 8 presidential election.

Carson made the announcement at a joint news conference with Trump in Florida, ahead of that state’s primary on Tuesday.