New presidential candidate to enter the race?

Weekly Standard's Bill Kristol says yes, and Donald Trump has been quick to issue his response

Weekly Standard editor Bill Kristol sent out a provocative tweet Sunday, suggesting that another presidential candidate -- an independent -- would be entering the race for the White House over the holiday weekend.

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

Kristol said no more Sunday evening, beyond the tweet, which referred to the yet-to-be-named candidate as "an impressive one, with a strong team and a real chance."

Donald Trump unleashed a series of tweets in response, insulting Kristol, and both badgering the GOP and calling on the party to unite against this unnamed new opponent. He also implied in his tweets that an independent run would mean a Clinton victory and a liberal nomination to the nation's highest court.

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

— Donald J. Trump (@realDonaldTrump) May 29, 2016

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!

— Donald J. Trump (@realDonaldTrump) May 29, 2016

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

• Commentary: Why #NeverTrump failed

The Washington Post had reported a little over two weeks ago that GOP operatives had mounted an effort to derail Donald Trump by bringing in another conservative candidate. CBS News' Julianna Goldman confirmed that several names were being considered at the time, including former Oklahoma Sen. Tom Coburn, former Secretary of State Condoleezza Rice and retired Army Gen. Stanley A. McChrystal.

Independents sense an opening -- Trump and Hillary Clinton have the highest unfavorable ratingsin CBS News/New York Times polls going back to 1984, when the question was first asked.

But the time for an independent candidacy is running short -- the deadline to make it onto the Texas ballot for the general election has already passed, and North Carolina's deadline is coming quickly on June 9.