Brash billionaire Donald Trump has pledged his loyalty to the Republicans, ruling out an independent run if he doesn't win the party's presidential nomination.
Trump made the announcement in the lobby of his New York headquarters on Thursday as he shot to an even greater lead in the polls, with 30 percent of the Republican-leaning vote.
"I will be totally pledging my allegiance to the Republican Party and the conservative principles for which it stands," the real estate tycoon told a news conference at Trump Tower.
"We will go out and we will fight hard and we will win.
"I see no circumstances under which I would tear up that pledge."
It marks an about-turn for the former reality TV star, who kicked off the first Republican debate in Ohio last month by refusing to rule out a third-party run.
His say-it-how-it-is attitude, business acumen and charisma have made him a rock star in the eyes of ordinary Republican voters, but his refusal to dismiss an independent run had confounded party grandees.
There had been widespread Republican fears that a third-party run could split the vote and hand the Democrats - and frontrunner Hillary Clinton - a free ticket into the White House.
Trump changed his mind because of his soaring poll figures, and said winning the Republican ticket was the "absolute best way" into the top job.
Trump - who lauds himself in his official biography as "a deal maker without peer" - said he got "absolutely nothing" in return for his pledge "other than the assurance I would be treated fairly".
He lauded his billions and financial independence as a unique buying point for the electorate, saying his alone was a self-funded campaign.
By contrast his chief rivals - Clinton and perceived establishment choice Jeb Bush for the Republicans - were in the pockets of lobbyists, he said.
"I will tell you this. Nobody's putting up millions of dollars for me. I'm putting up my own money," he said to applause.
Some commentators suggest securing Trump's loyalty may come at a heavy price for the Republicans if it antagonises those enraged by his more controversial opinions, particularly his insults towards illegal immigrants.
Trump denies that he is anti-immigrant, only anti-illegal immigration.
He suggests he wants to do more to help talented foreigners, such as tech entrepreneurs, engineers, physicists and the best performing foreign students stay in the country and acquire citizenship.
Trump on Thursday also repeated his love for boundary-pushing rapper Kanye West, who stole headlines at the MTV Video Music Awards by announcing he would run for president in 2020.
"I'll never say bad about him. You know why? He loves Trump," he said.
"I love him. Now, maybe in a few years I'll have to run against him.
"I only hit people when they hit me."