A serious independent candidate will step up to challenge presumptive Republican presidential nominee Donald Trump and likely Democratic standard-bearer Hillary Clinton, Weekly Standard editor Bill Kristol suggested on Sunday.

Just a heads up over this holiday weekend: There will be an independent candidate--an impressive one, with a strong team and a real chance. — Bill Kristol (@BillKristol) May 29, 2016



"Just a heads up over this holiday weekend: There will be an independent candidate — an impressive one, with a strong team and a real chance," Kristol said in a message on Twitter.

Kristol has been leading an effort to recruit an independent candidate to take on Clinton and Trump, who each have unusually high negative favorability ratings.

Later Sunday, Trump on Twitter tried to knock down the possibility of an independent challenger:

"Bill Kristol has been wrong for 2yrs-an embarrassed loser, but if the GOP can't control their own, then they are not a party. Be tough, R's!"

"The Republican Party has to be smart & strong if it wants to win in November. Can't allow lightweights to set up a spoiler Indie candidate!"

Bill Kristol has been wrong for 2yrs-an embarrassed loser, but if the GOP can't control their own, then they are not a party. Be tough, R's! — Donald J. Trump (@realDonaldTrump) May 29, 2016



"If dummy Bill Kristol actually does get a spoiler to run as an Independent, say good bye to the Supreme Court!"

The Weekly Standard editor has been calling for another independent challenger to emerge in the presidential race for more than a month, speaking about it most notably with Mitt Romney; former Republican Oklahoma Sen. Tom Coburn; and Republican Nebraska Sen. Ben Sasse. Over the past month, all three have ruled out running themselves but expressed support for someone else to make the move.

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It was not clear from Kristol's message whether the name of a candidate would be produced over the weekend or at an undisclosed date in the future. However, time for the purported candidate is already short. The deadline for making it on the November ballot in Texas passed on May 9. The next deadline is in North Carolina, where the candidate will need to provide about 90,000 signatures from supporters by June 9 in order to make it on the ballot.