WASHINGTON – Newtown. Charleston. Pulse. Parkland. Vegas.

America's most infamous mass shootings in the past decade have led to relatively little change to prevent gun violence. And mass shootings continue – 251 and counting so far this year.

Washington closed background reporting system loopholes, expanded federal aid for school safety and banned bump stocks in the aftermath of those massacres. But gun safety advocates say real solutions such as tighter background checks, an assault weapons ban and restrictions on high-capacity magazines were left off the table.

Now the question is whether the separate mass killings in El Paso, Texas, and Dayton, Ohio, that left a combined 31 dead and dozens more wounded over an early August weekend could be the spark that leads to significant change.

Advocates remain skeptical given President Donald Trump's ferocious defense of the Second Amendment and a Republican-controlled Senate that is strongly backed by gun rights groups. A POLITICO/Morning Consult poll released Wednesday found a clear majority back an assault weapons ban, but only 39% said they think it’s very or somewhat likely Congress passes gun control legislation in the next year.

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Senate Majority Leader Mitch McConnell, R-Ky., said Thursday he has no plans to call the Senate back from recess to vote on laws beefing up gun background checks despite demands for immediate action from more than 200 mayors, including those of El Paso and Dayton.

But the dialogue over larger changes such as "red flag" laws and beefing up background checks – issues Trump has indicated he's willing to consider – are giving gun-control groups hope that this moment might be different. At least in the long run.

That optimism is fueled by shifting political sands: internal strife at the National Rifle Association, the increasing clout and organizing power of the gun-control movement; a Democratic-controlled House willing to pass gun control measures such as background checks; moves by Corporate America in response to recent gun violence; a sense that a groundswell for gun control is growing.

McConnell said Thursday he's willing to have a conversation about background checks and red flag laws that give authorities more power to take firearms away from people deemed threatening. And Trump told reporters several times Friday he supports "meaningful background checks" though he did not offer specifics.

But those who have heard similar promises after horrific mass killings aren't expecting miracles any time soon.

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"We've been here before," said Lanae Erickson, senior vice president of Third Way, a center-left group that backs bipartisan gun control.

"I'm very optimistic about the direction of the conversation around guns over the next five years. I'm pessimistic that Mitch McConnell passes something in the next five weeks or five months," she said. "These shifts take time and they're happening. But McConnell is old-school and is not going to do something that is going to make his base angry."

While they have talked about compromise on gun violence, Republicans say the main culprits for gun violence have little to do with firearms: a breakdown of the family, violent video games and a lack of resources to monitor and help the mentally ill.

NRA CEO Wayne LaPierre, who reportedly spoke several times with the president in the days after the Texas and Ohio shooting, tweeted out his opposition to any legislation "that unfairly infringes upon the rights of law-abiding citizens."

"The NRA will work in good faith to pursue real solutions to the epidemic of gun violence in America," he tweeted. "But many proposals are nothing but 'soundbite solutions' – which fail to address the root of the problem, confront criminal behavior, or make our communities safer."

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That's unlikely to appease gun control advocates such as Charlie Mirsky, the political director of March for Our Lives, the grassroots organization that grew out of the Marjory Stoneman Douglas High School shootings in Parkland, Fla., in 2018. A supporter of an assault weapons ban, Mirsky said March for Our Lives is willing to give on some issues but not on others.

'We're compromising already by talking about just (red-flag) orders and background checks," he told USA TODAY Friday. "There are way more measures that need to be put into place that are necessary to save American lives. That being said, we're definitely not going to compromise over the bills that we've already compromised in being satisfied with.”

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Here are four areas gun control advocates support and their prospects for passage when Congress returns:

Background checks

The House has passed two bills and sent them to the Senate:

The Bipartisan Background Checks Act of 2019 (H.R. 8) would prohibit most person-to-person firearm transfers unless a background check can be conducted. It aims to close a potential loophole allowing the transfer of firearms without a background check at gun shows or between individuals.

The Bipartisan Background Checks Act (H.R. 1112) would extend to at least 10 days the amount of time firearms dealers must wait for a response from the background check system before the sale can proceed. Currently, they can make the sale if they haven’t received a response in three days.

Both bills passed with almost every Democrat and a handful of Republicans supporting the measures. But some analysts say it's doubtful tougher screening would have prevented either massacre.

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A bipartisan Senate bill authored by Democrat Joe Manchin of West Virginia and Pat Toomey of Pennsylvania is being held up as a possible compromise. It would expand background checks – now only applied to purchases from federally licensed gun dealers – to include gun shows and Internet sales. It would continue to exclude those between family members and friends who give or sell guns to each other.

The NRA has opposed the proposal in the past and there is no sign gun rights advocates have changed their position.

"Had Manchin-Toomey passed in the past and had been signed into law, that’s no guarantee that these shootings would’ve been prevented," Toomey told reporters this week. "But that doesn’t change the fact we ought to be making it as difficult as possible for people who don’t belong owning a firearm from obtaining one. So, I hope we’re at a moment where the atmosphere has changed.”

On Friday, Trump signaled potential support on the issue.

"There’s been no President that feels more strongly about the Second Amendment than I do," he said. "However, we need meaningful background checks so that sick people don’t get guns."

Red flags

Of the all the issues being discussed, this one holds the most potential for passage.

Trump has talked conceptually about supporting such bills that give authorities more power through an emergency protective order process to intervene if they think an armed individual could be plotting to do harm.

A bipartisan Senate bill drafted by Republican Lindsey Graham of South Carolina and Democrat Richard Blumenthal of Connecticut would encourage and help states to set up red flag programs of their own.

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Gun safety advocates say it wouldn't do much because the states that would adopt such a program already have done so. The bill being discussed would not require such programs nationwide but its recognition of states' rights gives it a chance to win bipartisan passage.

What could give the legislation a boost, Erickson said, are reports the mother of the El Paso shooter contacted police in Allen, Texas, (where the shooter lived) weeks before the rampage out of concern that her son had a "AK"-type rifle.

"This tragedy has a different feel because we know there was something that should have stopped it," Erickson said. "When we've seen real movement, it's usually where there's a nexus between the gun safety law that we're talking about and that specific shooting and we have that here."

Sen. Rob Portman, R-Ohio, believes red flag laws address two facets of preventing mass shootings.

“There are some laws that I think bridge this issue of the guns and the mental health issue, and I think red flag laws is one,” he said.

Assault weapons ban

The latest shootings have revived talk on banning assault weapons, usually defined as military-style, semi-automatic firearms capable of killing large number of people quickly.

A POLITICO/Morning Consult poll released Wednesday shows nearly seven of 10 respondents back a revival of the ban on such weapons that expired in 2004 and was never renewed.

Advocates are encouraged that a House bill authored by Rhode Island Democrat David Cicilline to reimpose the ban has already attracted nearly 200 co-sponsors, including five lawmakers who signed on after the shootings in El Paso and Dayton.

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But there are no Republican co-sponsors and it's uncertain whether it would even receive the 218 votes in the House if it came up for a vote. Even if it did, the Senate wouldn't take it up and Trump wouldn't sign such a bill if it reached his desk.

"We're not looking at that right now," Trump told reporters Friday.

Large Capacity magazines

Usually paired with an assault weapons ban, a separate proposal limiting some types of ammunition sales also has little chance of passage any time soon.

Large capacity magazines, some of which can hold up to 100 rounds of ammunition, were used in Dayton and El Paso, as well as other mass shootings, including Las Vegas, Parkland and Sutherland Springs, Texas.

They "significantly increase a shooter’s ability to injure and kill large numbers of people quickly because they enable the individual to fire repeatedly without needing to reload," according to the Giffords Law Center.

Dayton shooter Connor Betts' use of a high-capacity magazine enabled him to kill nine and wound 27 others in the space of 32 seconds.

The gun control organization is named after former Arizona congresswoman Gabby Giffords, who was wounded during a 2011 shooting near Tucson.

The POLITICO/Morning Consult poll found 72% of respondents favor prohibiting the sale of high-capacity magazines, which became available after a ban on their sale expired in 2004.

The shootings prompted Rep. Diana DeGette to renew her call for passage of legislation that would prohibit the sale or use of such magazines.

The bill would not apply to high-capacity magazines already legally owned before the bill is enacted, or to any military or law enforcement officers who use high-capacity magazines as part of their jobs.

High-capacity magazines are banned in nine states - including California, Hawaii and New York - and Washington, D.C. Most of the states define high-capacity magazines as being able to hold 10 rounds of ammunition or more.

Contributing: Nick Penzenstadler