A handful of Senate Republicans on Tuesday dealt a severe blow to prospects for overhauling the criminal justice system in Congress this year, with one lawmaker calling the bipartisan legislation championed by President Barack Obama and some prominent conservatives “a massive social experiment in criminal leniency.”

The opposition from Sen. Tom Cotton, R-Ark., and others will make it difficult for proponents to push the bill as Senate Majority Leader Mitch McConnell, R-Ky., assesses GOP support. Backed by the White House and a coalition of conservatives and liberals, supporters had hoped it would be a rare legislative accomplishment in a fiercely partisan election year and a final piece of Obama’s legacy.

At an event for congressional staff, Cotton and Sen. Jeff Sessions, R-Ala., joined a group of federal prosecutors and argued against the bill, which would allow judges to reduce prison time for some drug offenders. The two senators — along with Sens. Orrin Hatch, R-Utah and David Perdue, R-Ga. — also issued statements of opposition.

Cotton later stood on the Senate floor, warning his colleagues that they would be held accountable if criminals were released and committed more crimes.

“If supporters of this bill and President Obama are wrong, if this grand experiment in criminal leniency goes awry, how many lives will be ruined?” Cotton asked. “How many dead? How much of the anti-crime progress of the last generation will be wiped away for the next?”

The bipartisan legislation, passed by the Senate Judiciary Committee in November, would give judges discretion to give lesser sentences than federal mandatory minimums, eliminating mandatory life sentences for three-time, nonviolent drug offenders. It also would create programs to help prisoners successfully re-enter society. The idea is to make the sentencing system fairer, reduce recidivism and contain rising prison costs.

Disparate voices — from Obama and the American Civil Liberties Union to the conservative Koch Industries — have said the system is broken and have backed the Senate bill.

In 1980, the federal prison population was less than 25,000. Today, it is more than 200,000.

Supporters of the bill are considering some changes to win over opponents, even though they sharply dispute the charge that the legislation would let violent criminals out of prison. Under the Senate bill, each case would be reviewed by a judge before the prison sentence was reduced.

Possible changes include revising or eliminating parts of the bill that would allow judges to consider reduced mandatory minimum sentences for violent offenders or criminals who had possessed a firearm.

“How those changes will look is still being determined, but we’re moving ahead to get a bill ready to be considered on the Senate floor,” Senate Judiciary Committee Chairman Chuck Grassley, R-Iowa, said in a statement Monday with Democratic Sen. Dick Durbin of Illinois, another supporter.

Cotton said he has been talking to staff as they look at changes, but still believes the legislation is based on a “false premise” that those who would be released are low-level, nonviolent offenders. Cotton and others have been more supportive of the prison reform piece of the bill that helps prisoners re-enter society.

The Arkansas senator is talking to Senate colleagues individually as advocates rally McConnell to move the bill this year. Cotton’s lobbying pits him against Texas Sen. John Cornyn, the No. 2 Republican in the Senate. Cornyn has been pressing his colleagues to support it, saying that opposition from Cotton and other conservatives like Republican presidential candidate Ted Cruz, who has similar concerns, is misplaced.

As conservative opposition has grown, Cornyn and House Majority Leader Kevin McCarthy, R-Calif., have said the legislation doesn’t have to move this year. Unlike McConnell, House Speaker Paul Ryan, R-Wis., has said the legislation is a priority, but hasn’t committed to a timeline.

The House Judiciary Committee has approved several separate criminal justice bills, with the eventual goal of moving them separately or together on the House floor. The panel plans to consider additional legislation later this week.

(AP)