Donald Trump, the top contender by a mile in the Republican 2016 presidential race, dropped his threat to run a third-party campaign by signing a loyalty pledge to support whoever wins the nomination -- even it is not him.

Trump -- noted for his dealmaking skills -- previously said his refusal to say he would not bolt the party was leverage to make sure he was treated with respect by GOP leaders. The threat of a Trump independent candidacy struck fear in many Republicans who remember how billionaire Ross Perot's campaign got 19% of the 1992 general election vote, siphoning support from George Bush and helping Bill Clinton take the White House.

The agreement comes at a time when Trump has what could be called a commanding lead in the field of 17. He sits far at the top of most national polls and is leading in key early states.

Trump the negotiator has calculated that as the frontrunner the pledge will add pressure on the other rivals to back him if he is the Republican nominee, a Republican source briefed on the agreement told the Post. It could also help win support from Republicans who have been slow to accept him because of his threat to run as an independent.

Tracking 149 polls from 29 pollsters nationwide/HuffPost Pollster #GOP pic.twitter.com/slsvuxcEhF

-- Donald J. Trump (@realDonaldTrump) September 2, 2015

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