“One big hurdle for our nominee will be to overcome the stereotype that Democrats want to take away everyone’s guns,” said Catherine Crooks, the Democratic Party chairwoman in Franklin County, population 10,124. “That isn’t the goal, the goal is responsible gun ownership. It needs to be made quite clear.”

Instead of articulating differences on gun control, the candidates are aiming to demonstrate their commitment to the issue through emotional displays.

Gov. Steve Bullock of Montana speaks about losing his 11-year-old nephew to a 1994 school shooting in Butte, Mont. Ms. Gillibrand describes her conversion from an N.R.A.-backed member of Congress to a gun control proponent by talking about meeting with mothers of gun violence victims in Brooklyn after her 2009 appointment to the Senate.

And at the annual Wing Ding dinner Friday night in Clear Lake, Iowa, Representative Tim Ryan of Ohio, who is currently an afterthought in polls, brought the crowd to its feet by recounting a bus trip he took last week to Kentucky, where he protested Senator Mitch McConnell’s refusal to hold a vote on legislation that would expand background checks.

“We took the fight to his backyard, telling him that we need gun reform in the United States of America and we need it now. We need it now,” Mr. Ryan said. “People are dying on the streets of this country, getting killed by weapons that were made for battlefields, not neighborhoods and places like Dayton, Ohio.”

Former Gov. John Hickenlooper of Colorado, who enacted expanded background checks and limits on the size of ammunition magazines in his state after a 2012 shooting that killed 12 at a movie theater in Aurora, Colo., said the N.R.A. would caricature whoever wins the nomination as a gun-grabber, so Democrats may as well offer an assertive platform.

Mr. Hickenlooper is familiar with the N.R.A.’s influence: It backed a successful recall campaign in 2013 to remove from office two Democratic state senators who voted for the new laws.