US presidential candidate Ted Cruz has won the backing of former rival Jeb Bush as prominent Republicans try to force a standoff with insurgent Donald Trump at their party's convention in July.
The endorsement by Mr Bush, part of a Republican dynasty, is the latest sign of how keen the party's establishment is to stop Mr Trump, fearing that his rhetoric on illegal immigration and national security will cost the party votes at the November 8 presidential election.
Mr Cruz, a US senator from Texas, is a staunch social conservative and a divisive figure in the party due to his willingness to criticise the leadership and his prominent role in bringing about a 2013 government shutdown.
But he is still seen by party grandees and many Republicans in Congress as preferable to Mr Trump, a real-estate billionaire viewed as straying even further from party orthodoxy.
"Republicans across the spectrum are realising that to nominate Donald Trump brings chaos to our party and potentially to our country," US Representative Trent Franks of Arizona told Reuters, "and that any differences they might have had with Ted Cruz are far less important than the danger of nominating Mr Trump."
In his customary style, Mr Trump took to social media to register his scorn, referring to the profligate spending by former Florida governor Bush's well-funded campaign and associated political fundraising groups.
"I think having Jeb's endorsement hurts Lyin' Ted," ran a message on Mr Trump's Twitter account. "Jeb spent more than $150,000,000 and got nothing. I spent a fraction of that and am first!"
Mr Bush, who quit his campaign last month after a poor start to the primary season, sent a fundraising email on Mr Cruz's behalf to his supporters, urging them to help "overcome the divisiveness and vulgarity" of Mr Trump.
Mr Cruz won the Republican caucuses in Utah on Tuesday but time is running out for him to defeat Mr Trump before the Republican convention in July, and for Republican establishment figures to reassert control of a party that is being wrested away from it by rank-and-file voters.
Mr Cruz looked on track to win all of the 40 Republican delegates from Utah, although Mr Trump won the 58 delegates up for grabs in Arizona, partly due to his tough message on illegal immigration.
After Tuesday, Mr Trump had 738 of the 1237 delegates needed to win the nomination, according to The New York Times. Mr Cruz had 463.