Republican front-runner Donald Trump - with pressure from the party - signed a Republican pledge on Thursday which sends a promise that he will not run as an independent candidate if he loses the Republican nomination for the 2016 elections.
The property tycoon waved the signed loyalty pledge in the air for TV cameras, during a news conference at his campaign headquarters in his own Trump Tower in Manhattan, New York.
"The best way forward, to win, is if I win the nomination and go direct against whoever (the Democrats) happen to put up. So for that reason, I have signed the pledge," Trump told reporters gathered at his campaign headquarters.
"I see no circumstances under which I would tear up that pledge," he said.
The Republican Party pledge requests from the presidential candidates to "endorse the 2016 Republican presidential nominee regardless of who it is."
"I will be totally pledging my allegiance to the Republican Party and the conservative principles for which it stands," Trump said on Thursday.
The billionaire business mogul, who has been soaring in the polls, has faced pressure during the recent weeks from the Republican Party and its chairman, Reince Priebus, to sign the pledge.
The RNC has since sought a loyalty pledge from each of its presidential hopefuls, in what is believed to be a first for the party, which saw a unanimous agreement to the pledge from all the 17 other Republican candidates, Priebus said in a statement later on Thursday.
His promise of allegiance regarded as a victory for the Republican National Committee (RNC) in its efforts to pull the billionaire into the party, which may have seen a split in its support and given the Democrats a boost had Donald Trump moved ahead as an independent candidate.
But the pledge appears to not be legally binding and does nothing to put an end to Trump's personal attacks against Republican rivals and stinging rhetoric on matters like immigration that have shaken up the entire nation for the nomination.
"I don't know what motivated Trump specifically, but the problem is that it's a non-binding deal," said Dave Carney, an unaligned Republican strategist in New Hampshire.
Carney added that the pledge could have some power during the primary process, since it is run by state parties, but during the general election, which will be organized by state governments, the pledge will ultimately have no binding authority.
Trump affirmed on Thursday that he received "absolutely nothing other than the assurance that I would be treated fairly" in return for signing the pledge.
During the Republican presidential debate last month, Trump was booed by audience members after he refused to dismiss the possibility of a third-party run; for he was the only candidate who rejected the commitment to back the winner of the party's primaries.
Criticism within candidates
Donald Trump has come under attack from his rivals in the race who have questioned his conservative credentials and liberal leanings in the past, almost two months after reaching the top of opinion polls among Republicans.
Reuters/Ipsos polling showed Trump with support among nearly 31 percent of self-identified Republicans as of Tuesday, with Bush at nearly 12 percent, following behind former neurosurgeon Ben Carson.
Former Florida Governor Jeb Bush said in a video on Thursday that Donald Trump's views on illegal immigration were "too pessimistic" and accused him of being a Democrat in disguise and holding liberal positions on abortion rights, taxes and healthcare, despite vowing to support his rival if he won the party race.
Some of the measures Trump has emphasised to fight illegal immigration, include raising visa fees as a way to pay for the building of a wall along the US-Mexican border and ending the automatic right to citizenship for US-born children of families living illegally in America.
Trump responded to Bush on Thursday in a statement saying, "I think that when you get right down to it, we're a nation that speaks English and I think while we are in this nation we should be speaking English," he said.
"Whether people like it or not, that's how we assimilate."
— Jeb Bush (@JebBush) September 3, 2015
In turn, Bush made fun of Trump's pledge by tweeting a photograph of a piece of paper with the words "Voted Republican since 1972," on it and signed by Bush.
Another of the Republican candidates, New Jersey Governor Chris Christie, said the Trump pledge was "just a little too much drama."