Leading conservative Bill Kristol says Donald Trump will be challenged for the presidency by a impressive independent candidate with a “real chance” of beating the Republican nominee.

In a tweet on Sunday evening, Mr. Kristol, an outspoken critic of Mr. Trump and editor of the Weekly Standard, a respected conservative magazine, did not give further details.

“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,” he said.

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

Reached for comment this morning, Mr. Kristol told CNN, "Still lots of I's to dot and T's to cross."

In a series of tweets, the real estate mogul called Mr. Kristol a “dummy” and an “embarrassed loser.” He then said Republicans can “say good bye to the Supreme Court” if an independent contender does materialize.

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

 Republicans who back Mr. Trump say that he at least has vowed to make conservative Supreme Court appointments.

But Mr. Kristol isn't impressed.

"Do you think that Trump appointees are going to overturn Roe v. Wade?" he said. "You really think Donald Trump is going to do more than any previous Republican president? He's going to appoint such conservative appointees that they are going to overturn Roe v. Wade?"

Mr. Kristol has said Mr. Trump has not given any thought to Supreme Court nominees.

"Who would be his top adviser? Chris Christie?" he asked. "Are you happy with Chris Christie?"

First Published: May 30, 2016, 5:12 p.m.
Updated: May 30, 2016, 5:16 p.m.