WASHINGTON -- Democrats said Tuesday that they are pushing toward a vote on expanded gun control measures as the nation reels from its second mass shooting in a week. U.S. President Joe Biden said "we have to act," but prospects for any major changes were dim, for now, in the closely divided Congress.

Senate Majority Leader Chuck Schumer vowed Tuesday morning to bring to the Senate floor legislation passed by the House that would require background checks for most gun sales and transfers. He said the Senate "must confront a devastating truth" after a lack of congressional action on the issue for almost three decades.

"This Senate will be different," Schumer, D-N.Y., said a day after a shooting at a crowded Boulder, Colorado, supermarket, killed 10 people, including a police officer. "The Senate is going to debate and address the epidemic of gun violence in this country."

While a Senate vote on new gun control would be the first in several years, Democrats do not have the votes to pass any significant reform. They are not even united themselves, as Sen. Joe Manchin, D-W.Va., told reporters Tuesday that he opposes the House legislation on background checks.

The Senate Judiciary Committee held a hearing Tuesday on proposals for gun control. It is unclear whether any of the bills up for consideration -- most of them involving more restrictive background checks -- would have made a difference in the Colorado case. A 21-year-old man charged with killing eight people in the Atlanta area last week had purchased a 9 mm handgun hours before the murders, prompting advocates to push for longer waiting periods for purchases.

In brief remarks responding to the shooting, Biden urged Congress to move quickly to close the loopholes in the background check system and to ban assault weapons and high-capacity magazines -- an effort that would be even more difficult to achieve politically. According to a police affidavit, the Colorado shooter had purchased an assault rifle six days earlier.

"It should not be a partisan issue," Biden said. "This is an American issue. It will save lives, American lives."

Sen. Richard Blumenthal, D-Conn., who has aggressively pushed for expanded gun control since the 2012 shooting at Sandy Hook Elementary School that killed 20 children and six educators, expressed optimism about the chances for new laws with Biden in the White House and Democrats controlling the House and the Senate. He called it "the dawn of a new era."

Reality is likely more complicated. Senate Democrats do not currently have deep enough support among Republicans to pass new gun control legislation in the 50-50 Senate, as they would need 60 votes to do so. While expanding background checks is generally popular with the American public, even with some conservatives, Congress has been unable to find a successful compromise on guns in decades, making it one of the most intractable issues in American politics.

The gun debate also highlights a larger difficulty for Senate Democrats as they try to move forward on gun legislation and other policy priorities of the Biden White House. With the filibuster in place, forcing a 60-vote threshold for most legislation, House-passed bills on issues like gun control and voting rights are effectively nonstarters unless Democrats secure significant GOP support.

Some Republicans hinted that they would be open to negotiations, though it was unclear if there were any real bipartisan discussions. Senate Republican Leader Mitch McConnell said he was opposed to the House legislation, but "I'm certainly open to the discussion."

Manchin and Republican Sen. Pat Toomey of Pennsylvania, who have worked together for years to find compromise on background checks, both said they were opposed to the House legislation, which would close loopholes to ensure background checks are extended to private and online sales that often go undetected, including at gun shows, with some limited exemptions for family and other scenarios. A similar version Manchin and Toomey proposed just after the Sandy Hook shootings included a broader set of exemptions than the House bill.

The House also passed a second bill to extend a certain review period for background checks from three to 10 days. Rep. Jim Clyburn, D-S.C., introduced the legislation after a shooter killed nine people at a Charleston, South Carolina, church in 2015.

Toomey said he would like to find legislation that could pass, but "that probably would require something that's a little bit different. So, we'll see if we can figure out how to thread that needle."

Manchin did not say whether he would restart negotiations, only that "we're going to try to do the responsible, reasonable thing."

Schumer and Connecticut Democratic Sen. Chris Murphy, a leading advocate for gun control, said they would meet this week to discuss a path forward. Schumer has not said when he will bring the House legislation up for a vote.

Democrats say they feel the environment around gun legislation has evolved, especially since that last major push in 2013. They point to troubles at the National Rifle Association, the long-powerful advocacy group that poured tens of millions of dollars into electing Donald Trump in 2016. The organization has been weakened by infighting as well as legal tangles over its finances.

"This is the moment to make our stand. NOW," tweeted Murphy as details of the Colorado shooting emerged Monday evening. "Today, our movement is stronger than the gun lobby. They are weak. We are potent. Finally, a President and a Congress that supports gun reform."

Democrats are hoping there is a gradual political shift among voters as well. A Pew Research Center poll in September 2019 showed a wide majority of Americans, 88%, supported making private gun sales and sales at gun shows subject to background checks, which is what the House-passed bill would do. Ninety-three per cent of Democrats and 82% of Republicans were in favour of the policy.

Many in the GOP base are still strongly opposed to gun control of any kind. In Tuesday's hearing, which was scheduled before the Colorado shooting, Republicans showed no signs of wavering. Texas Sen. Ted Cruz said that every time there is a shooting, the Senate engages in "ridiculous theatre," with Democrats proposing laws that he said could take guns away from law-abiding citizens. Republicans have argued that background checks would not stop most mass shootings and would prevent some lawful gun owners from purchasing firearms.

"We already know this pattern is predictable, over and over and over again," Cruz said.

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Associated Press writers Lisa Mascaro, Hannah Fingerhut and Michael Balsamo contributed to this report.