A boy who chose not to give his name sizes up an assault-style rifle during the National Rifle Association's annual convention on May 3, 2013, in Houston. (Steve Ueckert/Associated Press)

In September 2004, as the expiration date approached for the federal assault weapons ban, Sen. John F. Kerry (D-Mass.) called on Congress to renew it. As a junior senator, he'd supported the measure; as a presidential candidate, he knew that the Republican majority in the Senate was going to let it die. There was little appetite for a fresh debate on gun rights, but for a few days, Kerry tried to have one, arguing that the ban could be saved if the president showed leadership.

"In the al-Qaeda manual on terror, they were telling people to go out and buy assault weapons, to come to America and buy assault weapons," Kerry said at a rally in Missouri. "Every law enforcement officer in America doesn't want us selling assault weapons in the streets of America. But George Bush, he says, 'Well, I'm for that.' "

Bush's campaign dismissed Kerry as an opportunist. "To infer that the president is helping terrorists is a clear example of a desperate candidate," campaign spokeswoman Tracey Schmitt said.

The 1994-2004 ban expired, and in 2008 and 2012, there was no similar campaign by Democrats to promote an assault weapons ban. But in interviews since the Orlando shootings, Hillary Clinton has called for the ban to return, and linked the easy availability of semiautomatic weapons to terrorism.

"We’ve got to keep weapons of war off our streets, as well as blocking suspected terrorists from buying guns," the presumed Democratic presidential nominee said Monday on "CBS This Morning."

The day after the Orlando shooting, GOP candidate Donald Trump railed against the president and warned Muslims should be banned from entering the U.S., while Democratic rival Hillary Clinton called for changes to gun laws. (Sarah Parnass/The Washington Post)

It was not a new position for Clinton. She had voted with Kerry to extend the old assault weapons ban; last year, she called for a new ban. Her 2015 proposal was read as evidence that she was more interested in capturing the center-left Obama coalition than in appealing to conservative Democrats. A Washington Post-ABC News poll that had tracked voter opinion of the ban had support above 70 percent when Congress let it expire, but just 45 percent in 2015.

Increasingly, Democrats wonder whether the threat of terrorism will change that. "The fears have certainly been borne out," said Bob Shrum, Kerry's 2004 campaign strategist. "The issues are more salient today than they were then, because the focus then was on dangers overseas. You had President Bush saying, 'We're fighting them over there so we don't have to fight them here.' You don't hear that anymore."

Kerry, Shrum said, did not start talking about assault weapons because it polled well. "We had no expectation that it was politically powerful," he said. "It’s more powerful now because we have a combination of domestic terrorism and an ability to go into any gun show and buy an AR-15."

The first decade after the ban expired suggested that its political potency had run out. In 2013, Sen. Dianne Feinstein (D-Calif.) offered a modified assault weapons ban as part of the doomed post-Newtown gun safety package. It won just 40 votes, losing 15 Democrats, mostly from Western states and red states. Democrats thought they'd found a better angle on the terrorism issue in 2015, when all but one of them, Sen. Heidi Heitkamp (D-N.D.), backed an amendment to a health-care bill that would have prevented people on the FBI's watch list from obtaining guns. Clinton, whose electoral map does not include some of the red states where Democrats have been tripped up on gun votes, has signaled that she would go much further.