“Never,” said Chris Schrimpf, a spokesman for Gov. John Kasich of Ohio, who is still running against Mr. Trump. “No chance.”

“Hahahahahahahahaha,” wrote Sally Bradshaw, a senior adviser to Jeb Bush, when asked if he would consider it.

“Scott Walker has a visceral negative reaction to Trump’s character,” said Ed Goeas, a longtime adviser to the Wisconsin governor.

Or, as Senator Lindsey Graham put it, “That’s like buying a ticket on the Titanic.”
A remarkable range of leading Republicans, including Gov. Nikki Haley of South Carolina and Senator Jeff Flake of Arizona, have been emphatic publicly or with their advisers and allies that they do not want to be considered as Mr. Trump’s running mate.