Which Donald J. Trump will show up at Thursday night’s Republican debate in Cleveland?

There’s the Trump who calls the other GOP candidates “clowns” and responds to criticism with schoolyard insults. Then there’s the Trump who last week tweeted about the coming debate: “it is certainly my intention to be very nice & highly respectful of the other candidates.” Mr. Trump seems to have recognized that as the candidate atop the Republican heap, he now will be held to a higher standard than he was as a celebrity polling in low single digits.

Even more interesting than the style Mr. Trump brings to the stage is what opinions he has with him. Over the years he’s held many conflicting positions on many important issues.

Will the Trump who walks on stage Thursday night be the one who in 1999 told CNN’s Larry King that “I’m quite liberal and getting much more liberal on health care”? The one who wrote in his 2000 book, “The America We Deserve,” that the U.S. should consider a single-payer health system like Canada’s government-run plan? That system “helps Canadians live longer and healthier than Americans,” this Trump wrote. “We need, as a nation, to re-examine the single-payer plan, as many individual states are doing.” Or will debate viewers instead get the Donald Trump who earlier this year called ObamaCare a “filthy lie” and “total catastrophe”?

To continue reading Mr. Rove's column in the Wall Street Journal, click here.

Karl Rove joined Fox News Channel as a political contributor in February 2008. He also currently serves as a columnist for the Wall Street Journal. Mr. Rove helped organize the political-action committee American Crossroads. His latest book is "The Triumph of William McKinley: Why the Election of 1896 Still Matters" (Simon & Schuster, 2015). Follow him on Twitter @KarlRove.