Former US president George HW Bush has called on Republicans to rally behind frontrunner Mitt Romney and wrap up the party's presidential nominating process.
"We've known Mitt for a long time and he's the man to do this job and go on to win the presidency," Bush told reporters gathered in his Houston office, with his wife Barbara and Romney at his side.
"I do think it's time for the party to get behind Governor Romney," Bush said.
Quoting lyrics from the classic Kenny Rogers song, The Gambler, the former president said: "There's a time to hold them and time to fold them. There is a time for people to get behind this good man."
The endorsement comes amid concerns that a prolonged primary battle leading all the way to the national nominating convention could ultimately hurt Republican chances to defeat Democratic incumbent Barack Obama in November.
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Bush's son Jeb Bush, the onetime governor Florida and another heavyweight in the Republican establishment, announced his support for Romney last week. Another son, former president George W. Bush, has yet to make an endorsement.
Senator Marco Rubio, a rising Republican star also from the key battleground state of Florida, threw his support behind Romney on Wednesday.
"Having your support means a great deal to me on a personal basis, on a family basis and also on a national basis," Romney told Bush.
"I look forward to being successful and honouring that endorsement by winning."
Romney is ahead in the nomination race with 565 delegates, followed by Rick Santorum with 256, Newt Gingrich with 141 and Ron Paul with 66, according to the Real Clear Politics website.
A candidate needs 1,144 delegates to clinch the nomination.
