Former Republican presidential candidate Jeb Bush has endorsed Texas Senator Ted Cruz for president, calling him a “principled conservative”.
Mr Bush, former governor of Florida, dropped out of the race last month after poor showings in state contests.
He said Mr Cruz has shown the ability to appeal to voters and win primary contests, like in Utah on Tuesday.
Republicans must “overcome the divisiveness and vulgarity” Donald Trump has introduced, he said.
If not, the party will certainly lose the White House to Democratic front-runner Hillary Clinton, Mr Bush wrote in a Facebook post.
“Republicans can win back the White House and put our nation on a path to security and prosperity if we support a nominee who can unite our party and articulate how conservative policies will help people rise up and reach their full potential,” he wrote, and linked to Mr Cruz’s website.
Mr Cruz, speaking to CNN on Wednesday, said Mr Bush’s endorsement proved his candidacy had garnered support among Republicans.
Former 2012 Republican presidential candidate Mitt Romney also recently endorsed Mr Cruz, strongly urging fellow Republicans not to back Donald Trump, a billionaire businessman from New York with no prior political experience.
Mr Trump, the party’s front-runner, currently has the highest delegate count and has said there may be “riots” if he is denied the Republican nomination come the party’s convention this summer.
Anti-Trump Republicans are hoping for a brokered convention, in which party officials, not delegates, would chose the nominee, but that is only possible if Mr Trump falls short of the 1,237 delegates needed to secure the nomination.
After contests in Utah and Arizona on Tuesday, Mr Trump has 739 delegates and Mr Cruz has 465.
Former Republican presidential candidates Carly Fiorina and Lindsey Graham have also endorsed Mr Cruz.
Mr Cruz has urged Ohio Governor John Kasich to drop out of the race, and said he would probably find a place for him in his administration.
He said Mr Kasich was a “spoiler” by taking votes that could go to him and help the Republicans defeat Mr Trump.
The nasty battle between the leading Republicans worsened this week when Mr Trump warned Mr Cruz he would “spills the beans on your wife” after an anti-Trump group ran ads in Utah featuring a racy photo of Mr Trump’s wife Melania from an old GQ magazine spread.
Mr Cruz said in response: “Donald, if you try to attack Heidi, you’re more of a coward than I thought.”
