After downplaying the issue for most of the past two decades, Democrats in Congress and on the presidential campaign trail are now advancing their most ambitious ideas to control access to firearms since at least the 2000 election, and arguably ever.

The new proposals range from a near-universal call from the field of 2020 presidential candidates to ban assault-style weapons and high-capacity ammunition magazines to proposals from several candidates to require licensing of gun owners and registration of either all guns or assault weapons. Neither Democrats nor the leading gun control groups have seriously discussed licensing or registration since the 2000 presidential campaign, when Al Gore endorsed the former and many (including former President Bill Clinton) later partially blamed his loss to George W. Bush on the vice president's positions on guns.

This reversal reflects the greater unity on gun-related issues that Democrats have achieved over the past few years as their electoral coalition has shifted away from heavily blue-collar and rural areas, where gun culture is strong, toward urban centers and white-collar suburbs that generally support limits on access to firearms. Particularly with their push to require background checks for all gun sales, Democrats are now much more confident than even a few years ago that they hold the upper hand on gun issues, particularly against the remaining Republicans in the House or Senate who must appeal to substantial suburban constituencies.

But the proliferation of proposals to regulate gun ownership, particularly from the presidential candidates, threatens to divide Democrats along lines familiar on other issues, from immigration to health care.

Liberals and gun control advocates generally argue it's important to shift the parameters of the debate with sweeping ideas like licensing of gun owners, even if they have little chance of passing Congress in the near term. Peter Ambler, executive director of Giffords, the gun control advocacy group co-founded by former Rep. Gabby Giffords, an Arizona Democrat, believes a more aspirational presidential debate can generate momentum for more immediate legislative priorities.

"The folks that have been skeptical about the politics of gun safety for a long time are the same ones who feel the gun debate needs to happen within the four corners of a compromise amendment from six years ago," he said, referring to the 2013 Senate vote on universal background checks. "The debate that we're seeing happen at the national level, whether we're talking about presidential politics or Congress, is derived from the fact that voters across the country are extremely angry at the status quo. ... The fact that our leaders are responding to that anger is of enormous benefit to our legislative efforts and doesn't distract (from them) in any way, shape or form."

But moderates fear that Democrats pushing the most sweeping ideas risk alienating centrist voters who are ambivalent or uneasy about President Donald Trump's tumultuous term.

"Political concerns about gun safety measures aren't as acute as they were in 2000, but they're not completely gone," said Matt Bennett, executive vice president for public affairs at Third Way, a centrist Democratic group. "Even a diminished NRA is dangerous. More importantly, we don't want to write Trump's ads for him. Overreaching on an issue as charged as this is a bad idea in an epochal election like this one. It won't help us win the blue wall states we need to defeat Trump, and it certainly won't help us win states like Colorado, Arizona, Maine and Alabama to give a Democratic president a governing majority in the Senate."

Momentum grows, then slows

The long-term arc of greater Democratic ambition on gun control offers one of the most dramatic measures of how the party's shifting electoral coalition has changed its incentives on issues that divide the country along cultural lines.

In the early 1990s, when Congress last seriously addressed gun control issues, Democrats still relied heavily on working-class and rural white voters, both in Congress and in their presidential voting coalition. That made gun issues a point of often-bitter division within Democratic circles.

When the Democratic-controlled Congress and Clinton passed the Brady Bill in 1993 requiring background checks for firearm purchases made in gun stores, 69 House Democrats -- almost all representing rural, blue-collar or Southern districts -- voted no. When Congress and Clinton passed an assault weapon ban in 1994, 77 House Democrats, almost entirely from the same constituencies, voted no. Both bills passed only because a substantial number of suburban House Republicans crossed over to support the measures.

The November 1994 landslide that swept the GOP to control of both the House and Senate discouraged Democrats from pressing gun control issues for most of the remainder of the decade. After the massacre at Columbine High School in April 1999, Clinton put the issue back on the front burner. He proposed a package of gun control initiatives that included universal background checks, or what was then known as closing "the gun show loophole" that allowed sales at such events to occur outside of the review system established under the 1993 bill.

The Republican-controlled Congress rejected Clinton's ideas but they renewed momentum in Democratic circles that carried into the 2000 presidential race. Challenging Gore for the nomination from the left, former Sen. Bill Bradley of New Jersey painted him "the poster boy" for the National Rifle Association.

Both men supported Clinton's proposal for universal background checks and extending the ban on assault weapons. Bradley also proposed what was seen as an extremely confrontational idea: requiring that all handgun owners obtain federal licenses and all guns be registered with the government. Responding to that pressure, Gore embraced what was seen as the somewhat less polarizing idea of requiring licensing only for new handgun purchasers and not addressing registration at all.

But Gore retreated even from that proposal in the general election. At that point, Democrats still relied upon rural and blue-collar white voters in larger numbers than they do now, and he clearly lost faith in the licensing plan when it came under attack from Bush and the NRA. As I wrote at the time , "In his second (national) debate with Bush, Gore never mentioned his centerpiece proposal -- the call for licensing new handgun owners -- until Bush criticized it; in the third debate, Gore redirected a question about gun control into a discussion of shrinking government so fast that viewers might have been wondering if he had a gun at his back."

Gore's narrow loss to Bush buried gun control in the Democratic Party even more emphatically than the 1994 GOP congressional sweep. After the election, Clinton told me that he believed Gore had lost the election in the places -- like Tennessee, Arkansas and northern New Hampshire -- where there were not enough union members for the AFL-CIO to offset the grassroots campaign the NRA had waged against him among blue-collar whites.

For more than a decade, it became conventional wisdom among Democrats that pushing for gun control amounted to electoral Russian roulette. Even when the party held unified control of the White House and Congress in 2009 and 2010, it did not seriously consider any gun control measures, largely because of concerns from its remaining rural and "blue dog" legislators.

Pressure for action grows

, and stressed the issue far more than he had. That changed only following the Sandy Hook school shooting just after Obama's reelection in 2012. A Republican-led Senate filibuster blocked Obama's renewed effort to pass universal background checks in 2013. But just as with Clinton's failed proposals following Columbine, the momentum carried into the next presidential race: Hillary Clinton ran in 2016 on the most ambitious gun control agenda of any Democrat since Gore in 2000and stressed the issue far more than he had.

Strikingly, even Trump's 2016 victory, with his massive margins among rural and working-class white voters, didn't squash the renewed interest in gun control among Democrats. The continued demand inside the party for action on guns partly reflected the impact of the grim cascade of mass shootings in recent years. But it also drew upon the undeniable new realities of the party's electoral coalition, which has grown stronger in metropolitan areas under Trump while losing ground in small towns and rural places, where the gun culture is strongest. The Democrats' greater consensus on gun issues was evident in February, when the House passed a universal background check bill with only two Democratic legislators -- both from largely rural districts -- voting no.

But the continued pulse of mass shootings -- most recently in El Paso, Texas, and Dayton, Ohio -- has, inexorably, generated pressure for further action. And that is pushing Democrats toward more precarious ground that tests their new consensus.

The first test of these boundaries will come on a renewed effort to ban assault weapons. Virtually every Democratic presidential candidate has endorsed restoring an updated version of the ban on assault weapons and high-capacity magazines that congressional Republicans and Bush allowed to expire in 2004.

The House Judiciary Committee has scheduled a mark-up for September 4 on legislation banning high-capacity magazines and a hearing for later that month on an assault weapons ban. House Democrats in swing districts have expressed considerably more anxiety about the assault ban than they did about the background check legislation. But the ban has been embraced by a critical mass of first-term Democrats and, at this point, 13 of the 31 House Democrats in districts that voted for Trump have co-sponsored the assault ban measure proposed by Rep. David Cicilline of Rhode Island. Overall the bill has 201 co-sponsors (including Republican Peter King of New York), and gun control advocates believe it could narrowly pass if brought to the floor -- though senior Democratic aides caution it does not yet have 218 votes.

The real debate among Democrats is whether it makes sense to hold a vote before 2020 on banning assault weapons since there's virtually no chance the Republican-led Senate will consider it. Some House Democratic leaders and gun control advocates don't want to shift the focus from the universal background check issue, which Trump and Senate Majority Leader Mitch McConnell, a Kentucky Republican, have faced growing pressure to address.

"What's helpful is focusing on McConnell and what we've already passed," said one senior Democratic aide who asked for anonymity to discuss internal deliberations. Others argue that an assault ban vote could put additional pressure on the last Republicans holding suburban seats around major cities -- including several in Texas -- and that failing to vote would strengthen the NRA by signaling that Democrats remain nervous about the issue.

The dynamic of the 2020 presidential race, though, is that an assault weapon ban -- an issue that was too hot for Obama to seriously address in either 2008 or 2012 and still faces a close call to reach a House majority -- is now just the starting point for the debate.

After the El Paso shootings, O'Rourke issued arguably the most sweeping proposal . He would require licensing and registration not only for all new gun purchases, but also for all existing gun owners, according to his national press secretary, Aleigha Cavalier. O'Rourke has also proposed a mandatory buyback for assault weapons already in circulation and a voluntary buyback for handguns.

, hasn't yet endorsed licensing or registration, but his aides don't rule it out. He's also embraced a ban on assault weapons and a buyback program, though he hasn't specified how it would work. Former Vice President Joe Biden, who is planning to release a comprehensive gun plan later in the campaignhasn't yet endorsed licensing or registration, but his aides don't rule it out. He's also embraced a ban on assault weapons and a buyback program, though he hasn't specified how it would work. His comments in an interview with CNN's Anderson Cooper suggest it would be voluntary, not a mandatory confiscation as O'Rourke is proposing.

Support among voters

Following the succession of mass shootings, polls consistently find substantial majorities for most of these ideas, particularly among constituencies that Democrats are targeting for 2020. Quinnipiac University polling in May found that 94% of registered voters supported universal background checks, 77% backed a licensing requirement and 63% endorsed a ban on assault weapons.

Of particular importance to the 2020 Democrats, those measures draw support not only from the party's core constituencies of minorities, young people and college-educated white women, but in the Quinnipiac polling at least 60% of college-educated white men and 66% of non-college white women also back each idea, according to detailed results they provided.

But pollsters in both parties caution that support for individual measures is only one indicator of how the gun control issue unfolds in practice. Also revealing is the overview question of whether voters worry more about protecting gun rights or regulating access to firearms.

On that question, an NBC/Wall Street Journal survey released Sunday , like many polls over the years, found the country much more closely divided: 45% of adults worried that policy would tilt too much toward restricting the rights of gun owners, while 50% were most concerned it would not do enough to control regulation of firearms. The results found significant fissures in both sides' coalitions: One-sixth of 2016 Hillary Clinton voters worried about infringing on gun rights, while an almost identical share of Trump 2016 voters worried that not enough would be done to regulate gun ownership.

Universal background checks draw a level of overwhelming support that is extremely rare in American politics on any issue. But beyond that, the evidence is that gun control tends to reinforce the geographic and demographic divides between the two major parties that the Trump era has already deepened.

For all the Democratic talk about regaining ground among rural and working-class white voters, the party's turn toward a more aggressive gun-control agenda makes that less likely, at least among the men in those categories. Conversely, it could help Democrats recapture some of the working-class white women who already show signs of drifting from Trump on other issues, from immigration to his personal behavior. (In the NBC/Wall Street Journal poll a slight plurality of them wanted more focus on gun regulation.) Simultaneously, the GOP's hard line against further gun control could deepen its distress among white suburban voters, especially women , already retreating from Trump.

Even if Democrats win back the presidency and recapture the Senate in 2020 while defending their majority in the House, all the gun-related ideas the Democratic presidential candidates are touting face a fundamental hurdle: Proposals such as a ban on assault weapons or high-capacity magazines -- much less licensing or registration of gun owners -- have virtually no chance of passing the Senate without ending the filibuster, which magnifies the influence of the small rural states most resistant to limiting gun ownership. That means if Democrats do regain unified control of government after 2020, gun control is likely to become one of the first skirmishes in a larger battle over whether the party can ever achieve its most ambitious goals while leaving the filibuster in place.