The U.S. Senate is on the verge of a bipartisan deal to strengthen sanctions against Russia — throwing an elbow at President Donald Trump, who has dismissed Moscow’s meddling in the 2016 election.

Their biggest stumbling block is how hard a punch to throw at Russia.

Democrats are pushing a harsh plan to let Congress block Trump from easing up current sanctions against Vladimir Putin’s government. But tying Trump’s hands on Russia may be too much of a rebuke for Republicans who have been loath to criticize the president even as he slams investigations into Russian electoral interference that threaten to derail their shared agenda.

A successful vote to punish Moscow would give a key win to Majority Leader Mitch McConnell (R-Ky.), a longtime Russia hawk who telegraphed his interest in a deal when he agreed to combine the issue with an Iran sanctions bill teed up for passage this week. If negotiators can’t agree on a strong Russia sanctions package, however, Minority Leader Chuck Schumer (D-N.Y.) has warned that Democrats would defect from an Iran bill that most of them otherwise support.

"Any member of the Congress who doesn't want to punish Russia for what they have done is betraying democracy," Sen. Lindsey Graham (R-S.C.) said Sunday. "And if the president doesn't sign the bill to punish Russia, he would be betraying democracy."

Foreign Relations Chairman Bob Corker last week predicted the Senate is “going to end up with something really, really strong on Russia that can be supported in a very bipartisan way," adding that “we understand all of the itches that are trying to be scratched” by senators furious about Russian cyberattacks during last year’s presidential election.

Corker also acknowledged to reporters that Trump’s administration, and any other, “obviously would not” want to see Congress force a legislative review of changes to Russia sanctions. Yet lawmakers set a precedent of sorts in 2015 when they forced then-President Barack Obama to submit his Iran nuclear deal for their eventual disapproval, the Tennessee Republican added.

The White House’s role in the Russia sanctions talks appears to lie in the eye of the beholder. Corker said Trump’s team has not gotten involved. One Democratic source described the administration as a “silent participant” in negotiations that include both parties’ leadership as well as senior Foreign Relations and Banking Committee members.

Staffers worked long hours last week on still-unresolved talks over the substance of the Russia amendment, which Corker said could include elements of as many as half a dozen bills. Democrats' top priority is a bipartisan proposal, which has two dozen backers on both sides of the aisle, to give Congress power to disapprove of any attempt to ease or waive sanctions.

The administration has sent mixed signals on its approach to Russia sanctions. Top White House economic adviser Gary Cohn said last month that “if anything, we would probably look to get tougher on Russia." But State Department spokeswoman Heather Nauert last week said “conversations are ongoing” about the return of two Russian diplomatic compounds the Obama administration shuttered in December as it unveiled new election-related sanctions.

“We are working to try to rebuild trust with the Russian government,” Nauert told reporters, describing “areas where we can work together,” chiefly in the fight against terrorism.

Asked if the White House would support the Senate’s proposed congressional review of any changes to Russia sanctions, spokeswoman Sarah Huckabee Sanders told reporters “the administration is committed to existing sanctions against Russia and will keep them in place until Moscow fully honors its commitments to resolve the crisis in Ukraine.”

“We believe that the existing executive branch sanctions regime is the best tool for compelling Russia to fulfill its commitments,” Sanders said.

But Democrats want to go further, adding new sanctions in response to what U.S. officials have largely described as a systematic Russian cyber-disruption campaign during the 2016 election.

“Since the Kremlin interfered in our elections, this is the most promising opportunity to pass sanctions legislation with teeth,” Sen. Jeanne Shaheen (D-N.H.), another key player in the sanctions talks, said through a spokesman. “There is bipartisan agreement that we need to seize this opportunity and get legislation over the finish line.”

And some Republicans are open to a double-barreled strategy that bolsters existing sanctions while adding new ones. Graham, the chief sponsor of the congressional review bill, told reporters Thursday on his way to a meeting on the Russia amendment that “I’m for both” his legislation and new sanctions against Moscow.

Trump himself remains the loudest skeptic of Moscow’s reported support for meddling in foreign elections, including alleged Russian complicity in hacks of French President Emmanuel Macron.

“Russian officials must be laughing at the U.S. & how a lame excuse for why the Dems lost the election has taken over the Fake News,” Trump tweeted on May 30.

Speaking to CBS' "Face the Nation" on Sunday, Graham vowed that if Trump doesn't sign this week's emerging Russia deal, "we're going to override his veto."

One potential sticking point may be merging a January Russia sanctions bill from Sens. John McCain (R-Ariz.) and Ben Cardin (D-Md.) with another bipartisan proposal from the Banking Committee’s leaders, Chairman Mike Crapo (R-Wyo.) and ranking Democratic Sen. Sherrod Brown of Ohio.

Crapo said that “unless we are able to negotiate” a mutually agreeable deal, he plans to introduce his and Brown’s sanctions bill as a separate amendment. That move risks setting up dueling sanctions votes, which Crapo admitted could hurt both proposals.

“I could definitely see a way that the two together might be stronger,” Crapo said.

Asked for his take on the bipartisan negotiations, Brown said only that they are proceeding positively.

The make-or-break moment for the Senate’s Russia sanctions vote is likely to come Monday, when McConnell plans to formally move onto the Iran bill to which any Moscow punishment would be attached. Republicans aim to finish the Iran bill this week, although Schumer warned Wednesday that his caucus would have a "very difficult" time voting to pass Iran sanctions absent a workable Russia agreement.

Even if the Senate can deliver a hard slap at Putin's government this week, however, the House would still have to clear the measure and send it to Trump's desk. Speaker Paul Ryan (R-Wis.) said in February that he would support turning Russia sanctions into law — if Trump made a move to ease them — but took a more cautious approach last week.

"I do think sanctions are called for in this particular case," Ryan told MSNBC, but "we already have them." Most importantly, he said, lawmakers "need to get to the bottom of exactly what were the sources and methods that the Russians used to try and undermine" elections before deciding how to move ahead.