On the other hand, Mrs. Clinton avoided speaking about gun control in rural white regions of Ohio, Pennsylvania and Kentucky, whose blue-collar voters will be desperately fought for by any Democratic nominee against Mr. Trump. A disparaging comment by Mr. Obama in 2008, who said that these voters cling to guns and religion, did much damage.

As Mrs. Clinton turns to the general election, she plans to highlight the issue in swing districts like Northern Virginia and the Philadelphia suburbs, a campaign official said, where changing demographics are tipping support for gun control, especially among women.

Mr. Trump’s naming of 11 potential Supreme Court justices on Wednesday seemed no coincidence: On the eve of the N.R.A.’s meeting, the group’s concern for the court’s conservative tilt is likely to outweigh any hesitations about Mr. Trump’s reversal from earlier liberal positions on gun control.

A statement on gun rights was one of the first detailed policy papers Mr. Trump issued last year after announcing his candidacy.

He accused Mrs. Clinton this month of seeking to “abolish the Second Amendment.” And just as he argues that casualties from the terrorist attacks in Paris last year would have been lower if civilians had been armed, he has proposed abolishing gun-free zones at military bases and at schools.

“I will get rid of gun-free zones on schools, and — you have to — and on military bases,” Mr. Trump said on the campaign trail in January. “My first day, it gets signed, O.K.? My first day. There’s no more gun-free zones.”

A federal law from the 1990s established gun-free school zones. It could not be reversed by executive order, as Mr. Trump seems to imply. (His campaign did not respond to a request for comment about his gun policies.)