WASHINGTON — A Republican policing bill stalled out Wednesday, blocked by Senate Democrats who dismissed it as meager “crumbs” in a vote that either signals the collapse of Congress’s efforts to respond to mass demonstrations over the killings of Black people or the start of fresh bipartisan talks toward compromise.

With a tally fell that almost exclusively along party lines, Congress reached a familiar impasse despite public outcry over the deaths of George Floyd, Breonna Taylor and other Americans. Polling shows the country overwhelmingly wants changes. But in the stalemate, for now, Democrats and Republicans are blaming each other as a generational crisis over racial injustice and police tactics explodes outside the doors.

“I’m frustrated,” said Sen. Tim Scott, the only Black Republican senator and the author of the GOP legislation.

“The issue is, do we matter?” he asked, echoing the words of the Black Lives Matter movement, during an impassioned Senate speech that drew applause from his colleagues. “We said no today.”

The outlook ahead is uncertain, as Democrats press forward Thursday with a House vote on their bill, a more sweeping package that is certain to be approved. Senate Majority Leader Mitch McConnell has vowed to try again before the July 4 recess. Yet swift action seems difficult.

With the standoff, the parties are settled into their political comfort zones, even if they are displeased with the actual outcome. Republicans are lined up squarely behind Scott, a uniquely credible voice in the chamber recounting his personal experience with racism at the hands of police. Democrats, led by House Speaker Nancy Pelosi and Senate Minority Leader Chuck Schumer, are standing with progressive and civil rights activists urging outright rejection of the Republican approach.