Congress returns to Washington this week after a summer recess punctured by a string of mass shootings under pressure to confront a uniquely American problem: how to combat the scourge of gun violence?

Though it has been a quarter of a century since Congress passed significant gun control legislation, Democrats and advocacy groups are displaying a fresh sense of resolve as major American retailers heed public calls for action in response to the recent wave of mass shootings.

After weeks of deliberation, Walmart announced it would stop selling ammunition for military-style assault rifles and no longer allow customers to openly carry firearms in their stores. In short order, Kroger, Walgreens, Wegmans and CVS said they too would discourage shoppers from openly carrying guns in their stores.

The response from corporate America followed back-to-back tragedies in El Paso and Dayton, Ohio, that left 31 people dead last month and a shooting in Odessa, Texas, that left seven people dead.

Now, activists say, it’s time for Washington to step up and stop politicians from lagging behind corporate America when it comes to gun reforms.

“When consumer-facing corporations make moves like this, there is no better statement of the shifting opinion of the American public,” said John Feinblatt, president of Everytown for Gun Safety. “Congress needs to pass a strong background check law and a strong red flag law. Anything less and the mood of the country will be ‘See you at the polling booth in 2020.’”

Everytown released new data on Friday indicating overwhelming support for new stricter gun laws. The poll found that 95% of Americans nationwide backed universal background checks and 85% favored the passage of so-called “red flag” laws, which are designed to prohibit individuals from purchasing firearms if they are deemed a threat to themselves or others. A 61% majority of Americans blamed gun violence on easy access to firearms.

“This broad public support shouldn’t come as any surprise to lawmakers,” Feinblatt said. “Just look back to November 2018 – if the midterms taught us anything, it’s that suburban voters resoundingly chose pro-gun sense candidates.

“They’re ready to vote out politicians who don’t take action to keep them safe.”

Congressional Democrats hope to create momentum by ramping up pressure on the Republican Senate leader, Mitch McConnell, to allow a vote on legislation passed by the House earlier this year that would strengthen and expand background checks.

Protesters call for firearms control and protest against gun violence, at a rally in Los Angeles on 17 August 2019. Photograph: Mark Ralston/AFP/Getty Images

“President Trump and Senate Republicans have failed to act on the issue of gun violence, bowing repeatedly to the NRA and the hard right by choosing inaction or half-measures over real, meaningful legislation,” the Senate minority leader, Chuck Schumer, wrote in a letter to members ahead of their return.

On Tuesday, the House speaker, Nancy Pelosi, will join members of the House Gun Violence Prevention Task Force at a forum to discuss McConnell’s “inaction on bipartisan House-passed bills to prevent gun violence”. Later next week, the House judiciary committee will prepare a slate of gun control bills to be brought to the floor for a vote.

The committee will consider a suite of measures that would ban high-capacity magazines, establish a federal grant program for states that implement red flag laws, and prohibit firearm sales to people convicted of certain misdemeanor hate crimes.

Meanwhile, the White House is engaged in a conversation with Senators Chris Murphy, a Democrat from Connecticut, Pat Toomey, a Republican from Pennsylvania, and Joe Manchin, a Democrat from West Virginia, about expanding background checks.

Senators Richard Blumenthal, a Democrat of Connecticut, and Lindsey Graham, a Republican of South Carolina, are also working with the White House on legislation that would offer grants to states that pass “red flag” laws.

It is unclear whether Trump supports any of these efforts. The president has repeatedly shifted positions on the issue, at some points expressing support for tightening background checks only to later backtrack and insist current laws are sufficient.

Where Trump lands on the proposals under consideration will determine the success of the latest push for gun reform in Congress. McConnell told the Hugh Hewitt radio show earlier this week that he would only hold votes on measures Trump was prepared to support.

“If the president took a position on a bill so that we knew we would actually be making a law and not just having serial votes,” McConnell said, “I’d be happy to put it on the floor.”

Yet at the congressional level, lawmakers remain intractably divided on how to respond, with Democrats advocating for gun control legislation and Republicans pointing to mental health and violent video games.

This is in stark contrast to the flurry of activity taking place in state legislatures to loosen or tighten gun regulations. In Texas, a day after the state was shaken by its second mass shooting in less than a month, a spate of new laws went into effect loosening restrictions on when and where firearms could be carried.

Mitch McConnell, the Senate majority leader, has said he will only bring gun control legislation to the vote if Donald Trump has indicated he backs it. Photograph: Jim Lo Scalzo/EPA

But there are signs the political battle lines are beginning to shift, even if it remains unlikely that the recent activism will produce a swift response from Congress.

“There is clearly a desire for Congress to do something – anything – to try to make the situation better,” said Whit Ayres, a Republican strategist. “Lawmakers on both sides of the aisle seem to agree that red flag laws and background checks are among the least difficult of the options on the table.”

On the 2020 campaign trail, Democratic hopefuls are going much further.

They have almost uniformly embraced bans on assault-style weapons and high-capacity ammunition magazines while some candidates have introduced ambitious proposals such as licensing for gun owners, registration for all guns purchased and a mandatory buyback program for assault weapons.

“Democratic presidential candidates have gone from running away from guns to running on guns,” said Kristin Goss, a Duke University political scientist who has studied gun control activism.

Goss said this reflects the party’s changing electoral coalitions. In the 1990s, when working-class, rural voters were still a key constituency, the party was bitterly divided over the issue and preferred to downplay it.

But now Democrats believe guns could be a defining issue in 2020, as they make gains with suburban voters, especially college-educated women fearful for their children’s safety in school.

“For the first time in more than two decades, we believe that guns could be an issue that matters in a real and positive way for Democrats,” said Matt Bennett, executive vice-president for public affairs at Third Way, a centrist Democratic thinktank.

But Bennett worries Democrats risk alienating voters frustrated with Trump’s presidency if they go too far with measures like licensing and gun buybacks.

“The danger is that we’re moving away from ideas that have near-universal support among voters to ones that have closer to 50% support,” Bennett said. “Congress hasn’t done anything for 25 years, so maybe we should start with something that’s universally popular.”

But many advocates believe the moment for bold reform is now.

“The center has shifted on this issue,” said Igor Volsky, executive director and founder of Guns Down America, which organizes for “a future with fewer guns”. “The approach we’re seeing now reflects the political reality and the political environment that we’re living in.”

Sabrina Siddiqui contributed reporting.