By Emily Stephenson
Republican candidate Donald Trump has won the endorsement of New Jersey Governor Chris Christie, who said the billionaire businessman had the best chance of beating Democrat Hillary Clinton in the November 8 presidential election.
"The best person to beat Hillary Clinton in November on that stage last night is undoubtedly Donald Trump," Christie told a news conference on Friday (local time), a day after a Republican candidates' debate.
He spoke at a news conference before a Trump rally in Texas.
Donald Trump is "rewriting the playbook," said Christie, 53, who until earlier this month was a Trump rival for the Republican Party nomination.
It was Trump's biggest endorsement from a mainstream Republican to date. The front-runner in the race, Trump, 69, has never held public office and has campaigned as a political outsider.
The endorsement of the New Jersey governor gives Trump, from neighbouring New York, a lift ahead of next week's crucial "Super Tuesday" nominating contests.
Trump, a brash former reality TV show host, has now won three straight nominating contests in New Hampshire, South Carolina and Nevada, convincing some mainstream Republicans that he may have too much momentum to be stopped, especially if he wins big in the key southern US primaries on Tuesday.
Former Secretary of State Hillary Clinton is battling US Senator Bernie Sanders of Vermont for the Democratic nomination.