WASHINGTON (AP) — Congress is hitting an impasse on policing legislation, as Senate Democrats on Tuesday opposed a Republican proposal as inadequate, leaving the parties to decide whether to take on the hard job of negotiating a compromise or walk away despite public outcry over the killings of Black Americans.

The standoff threatens to turn the nationwide protests over the deaths of George Floyd, Breonna Taylor and others into another moment that galvanizes the nation but leaves lawmakers unable to act. A new Associated Press-NORC Center for Public Affairs Research poll shows almost all Americans support some degree of criminal justice changes.

"This is a profound moment, it is a moral moment," said Sen. Cory Booker, D-N.J., a co-author of the Democrats' proposal. "The call is for us to act."

Yet Congress, as it has so many times before when confronted with crisis — on gun control or immigration changes supported by broad segments of the population — is expected to stall out, for now. Lawmakers are hesitant to make moves upsetting to voters as they campaign for election. And President Donald Trump, facing his own reelection, is an uneven partner with shifting positions on the types of changes he would accept from Capitol Hill.

Ahead of a test vote Wednesday, Senate Majority Leader Mitch McConnell acknowledged it may fall short. If so, he vowed to try again, hoping to pass legislation before a July 4 holiday recess.

"It's sad that this is falling along party lines," said Sen. Todd Young, R-Ind. "I hope that that changes."

The GOP's Justice Act would create a national database of police use-of-force incidents, restrict police chokeholds and set up new training procedures. It is not as sweeping as a Democratic proposal, which mandates many of the changes and would hold police liable to damages in lawsuits. The White House says an immunity provision is off the table.

Senate Democratic leader Chuck Schumer and top Democrats signaled they would oppose the Republican bill as "not salvageable," as they demand negotiations on a new, bipartisan package with more extensive law enforcement changes and accountability aligned with their own Democratic bill.

The Democratic opposition is being backed by the nation's leading civil rights organizations and the lawyer, Benjamin Crump, representing the families of Floyd and Taylor, two African Americans whose deaths in police interactions sparked worldwide protests over racial bias in policing.

"The Black community is tired of the lip service," Crump said in a statement.

As talks potentially continue, Democrats are trying to force Republicans to the negotiating table to strengthen Democrats' hand. The House is set to approve the Democrats bill later this week. The two bills, the House and Senate versions, would ultimately need to be the same to become law.

"We're ready to make a law, not just make a point," McConnell said as he opened the Senate on Tuesday. He said Americans "deserve better than a partisan stalemate."

But McConnell also said later that if the vote fails this week, he would take a procedural step to allow swift consideration again.

House Speaker Nancy Pelosi has indicated she is eager to enter talks with the Senate as they merge the Democratic and Republican bills, which is a signal that Democrats are not closing the door to a compromise.

Congress is under enormous pressure to establish new oversight and accountability of the police as demonstrations spill into cities large and small nationwide.

During Tuesday's Senate floor debate, Republicans insisted Democrats would have a chance to amend the Senate bill if they allow the debate to begin. But Democrats countered there is no agreement their changes would be up for consideration.

"Now is the time for Congress to pass legislation that will bring real change," said Sen. Kamala Harris, D-Calif., a co-author with Booker and House leaders on the Democratic bill.

Political risks of inaction are high, as the public wants to see changes after nearly a month of constant demonstrations in cities large and small that is forcing a worldwide reckoning over law enforcement tactics and racial injustice.

The NAACP Legal Defense and Fund is urging senators to vote against advancing the GOP package and push for changes .

"In this moment, we cannot support legislation that does not embody a strong accountability framework for police officers and other law enforcement who engage in misconduct as well as needed reforms to policing practices," the organization wrote to senators, according to a letter obtained by AP.

Crump, the attorney for the families, said the GOP package is "in direct contrast to the demands of the people, who have taken to the streets, to call for the reallocation of resources in order to improve social safety nets and public mental health programs."