Advocates for gun control are hoping to capitalize on momentum from massive March For Our Lives demonstrations over the weekend. But with opposition from pro-gun groups and Republicans in Congress, supporters say it won't be easy.

The day after hundreds of thousands of demonstrators packed protests in Washington, D.C., New York and sister marches around the Garden State, many are wondering: what now? During a radio appearance Sunday morning, Gov. Phil Murphy praised the demonstrators but said the gun lobby is a formidable foe.

"You can't underestimate the NRA," he said. "They're the most successful lobbying organization in the history of our country, unfortunately."

On Monday in Trenton, six gun control bills vetoed by former Gov. Chris Christie are up for a vote again. They include seizing guns from mental health patients and decreasing the maximum capacity of ammunition magazines. Gov. Murphy has promised he will sign them.

But New Jersey already has some of the toughest gun laws in the nation. And the governor said 80 percent of the gun crimes committed in the state occur with firearms coming from neighboring states. Advocates say national action is needed.

New Jersey native Capt. Mark Kelly is married to former Arizona Rep. Gabby Giffords, who was shot in 2011. In the aftermath, the couple became advocates for gun control. Kelly is optimistic things will be different this time because of the young people leading the fight.

"They realize this needs to be a bipartisan approach to change," he says. "So they get that and they're pretty much on message, they're smart, they're articulate, they also realize they have to motivate their peers to show up and vote."

With high schoolers leading the movement on gun reform nearing the voting age, supporters say there's reason for hope.

"This ain't over," says Gov. Murphy. "This is one major step in the right direction but there are a lot more steps to come and, in particular elections, have consequences."