Majority Leader Mitch McConnell (R-Ky.), center, Sen. John Barrasso (R-Wyo.), right, and Sen. John Thune(R-S.D.) address reporters earlier this year. (Bill O'Leary/The Washington Post)

Sen. John Hoeven had one question as he raised concerns in a private lunch about a criminal justice bill that has divided Senate Republicans: Why not make the changes requested by the National Sheriffs’ Association? 

Those revisions from the influential group could well tank a carefully crafted bipartisan compromise that already has President Trump’s seal of approval. But a growing number of GOP senators, who now control the fate of the bill, are seeking changes, growing uneasy with it or raising outright objections.

Though its supporters are claiming momentum behind the legislation that would mark a significant overhaul of U.S. sentencing laws, a large group of Senate Republicans are scrambling to get up to speed with one of Trump’s chief legislative priorities, even as they harbor private — and increasingly public — worries about the impact of the bill. 

“I have some of the same concerns that some of our conservative — some people who are opposed to it have voiced,” Sen. John Thune (S.D.), who will assume the party’s No. 2 position next year, said in an interview. Among the provisions giving him pause, Thune said, are the lifting of certain mandatory minimums and allowing for early release for some “pretty serious offenders.”

But “since it’s constantly being revised, it’s hard to know, exactly,” Thune added.

Laying out the dynamics of his 51-member conference, Thune said: “We’ve got people who are adamantly for it, strongly for it, people who are adamantly opposed to it and a lot of people who are asking the question, ‘Why now?’ ”

Hoeven’s comments at the closed-door Tuesday lunch were confirmed by the senator and people familiar with the remarks. In an interview before the lunch, Hoeven (N.D.) said the more law enforcement groups come on board with the bill, “the more it helps.” He said Wednesday morning that a number of Republicans want to push to include those changes outlined by the sheriffs’ group. 

The divisive nature of the criminal justice overhaul within the president’s own party could imperil what Trump has zeroed in as a top priority in the waning weeks of the year. The bill revises key sentencing laws by easing some mandatory minimum sentences and several other changes, while implementing efforts to help rehabilitate prisoners.

An unusual left-right coalition both inside Capitol Hill and among advocacy networks nationwide has aligned to support the legislation, the product of years of negotiation among a powerful core of Democratic and Republican senators. The House has passed a version of the legislation that doesn’t include the sentencing changes, but lawmakers there are confident it would quickly clear their chamber if the Senate does. 

But Senate Majority Leader Mitch McConnell (R-Ky.), well-attuned to the needs and concerns of his GOP ranks, is not eager to set up a vote on legislation that splits his conference. He has warned of the limited time this year for a vote, especially as lawmakers face more urgent tasks, such as preventing a partial government shutdown next week.

Earlier this year, McConnell had decided not to bring the criminal justice bill up for a vote until after the midterm elections, although its chief backers had a deal in principle back in August. 

The timing issue is one that is particularly irksome to some Senate Republicans who would like to support the bill but are wondering why Congress has to pass it this year, particularly with other must-pass priorities competing for lawmakers’ attention before the holidays.

“It’s a shame that this wasn’t ready for that type of discussion months ago, where we could’ve had that,” Sen. Ron Johnson (R-Wis.) said. “I personally think we’re so close, and I think the concerns that many members have could be addressed if we had the time to address it.”

The timing was central to the robust debate that unfolded Tuesday during the Senate Republican lunch, described by several senators who attended and GOP officials briefed on it. 

Several GOP senators, including Sens. Joni Ernst (Iowa); Lindsey O. Graham and Tim Scott (S.C.); and Rand Paul (Ky.) spoke in favor of the bill. Sen. David Perdue (Ga.) also spoke warmly. Sen. Tom Cotton (Ark.), a persistent critic of the bill, laid out his opposition — and was rebutted by Sen. Mike Lee (Utah), who has tangled with Cotton publicly on the issue.

In addition to Cotton, Sen. John Neely Kennedy (La.) argued against the substance of the legislation, while Sen. Ted Cruz (Tex.) also raised some objections. Johnson registered his concerns about the process and the timing, and Sen. Jon Kyl (Ariz.) similarly added: “I haven’t heard a plausible argument” for bringing the bill up.

Vice President Pence, a regular presence in the Senate GOP lunches, made the administration’s case in favor of the bill and also spoke approvingly of the criminal justice efforts in his home state of Indiana, which passed a major overhaul of its system in 2014. Jared Kushner, the president’s son-in-law and the White House official most closely allied with this issue, also attended the lunch, but he remained quiet and listened to the discussion. 

In public, opposition to the bill — whether a hard no or a softer position that encompasses concerns about the legislation — is starting to build among Senate Republicans. 

Along with Kennedy and Cotton, Sen. James E. Risch (Idaho) is also considered unpersuadable. Sen. Marco Rubio (Fla.) has said he opposes it as written. 

Meanwhile, Sen. Deb Fischer (R-Neb.) said in a brief interview that she is inclined to oppose the bill, citing concerns over the risk-assessment provisions in the bill. Johnson has similar concerns around that system, a process that helps determine how likely a prisoner is to reoffend. 

Sen. James M. Inhofe (R-Okla.) says he would support the bill if changes requested by Cotton is included. But that’s a highly unlikely proposition because Cotton is the bill’s most vehement opponent. 

With so many Republicans learning about the bill’s specifics, different senators give different assessments of where the conference broadly stands on the criminal justice measure. 

For instance, Scott said he counts 21 “hard” yes votes among Republicans and five more “soft” yeses. 

But elsewhere in the conference, the opposition is “big and intense, and very few Republicans understand why we would spend six legislative days, 11 calendar days, on the floor in a lame duck when we have to pass a spending bill, a farm bill, confirm a bunch of judges,” said one GOP senator who spoke anonymously to describe internal party dynamics. 

Still another GOP senator, who also requested anonymity, said: “Not as many (Senate Republicans) have problems as you would think.” 

The legislation’s authors aren’t completely ruling out changing the bill. But they are aware of the risk of rupturing the deal made with Democrats and the Trump administration, and aren’t eager to do so for the sake of just gaining more Republican votes if it’ll sap Democratic ones. 

“If I said to Senator Joe Blow that I was willing to accept his amendment, then I might lose 10 votes on the other side,” said Senate Judiciary Committee Chairman Charles E. Grassley (R-Iowa), the main Republican backer of the criminal justice overhaul. “That’s the art of compromise.”

Some Republicans believe the bill could potentially be revived next year, despite concerns that a new Democrat-led House may be emboldened to push for more dramatic changes to the sentencing system that would be unpalatable to Republicans.  

“I think most people in that room are sympathetic with what (is) being attempted,” Johnson said, referring to the GOP lunch. “They’re just not quite convinced this has got it right.”