There's been a stark partisan divide over the Trump dossier — the collection of "salacious and unverified" allegations about Donald Trump (the words are former FBI Director James Comey's) that was reportedly gathered by Trump's opponents, and later by the FBI itself, in both the Republican primaries and the general election.

Republicans believe the dossier is a key part of the Trump Russia story — after all, it involves a foreign intelligence agent (former MI6 agent Christopher Steele) digging dirt on Trump from Russians with possible ties to President Vladimir Putin. Democrats have not been very interested, preferring to focus on possible collusion between the Trump campaign and Russia and/or possible presidential obstruction of the collusion investigation.

Now, however, Republicans are heartened to hear Democrats expressing interest in learning just how the dossier came into being. It happened Thursday at the sometimes-dry Senate Judiciary Committee hearing on the Foreign Agents Registration Act.

The witness was William Browder, the businessman who crusaded for passage of the Magnitsky Act, which imposed sanctions on Russia after the killing of an anti-corruption lawyer. The sanctions enraged Putin, who retaliated by blocking American adoption of Russian babies. Putin also retaliated by launching a campaign to undermine and ultimately repeal the Magnitsky Act.

Among the Russians who took part in that campaign were Natalia Veselnitskaya and Rinat Akmetshin, who just happened to attend the June 9, 2016, Trump Tower meeting with Donald Trump, Jr. But the larger effort was organized by the American firm Fusion GPS, which denies any role in the Trump Tower meeting but was a big part of the anti-Magnitsky Act campaign.

"Veselnitskaya, through [the law firm] Baker Hostetler, hired [former Wall Street Journal reporter] Glenn Simpson of the firm Fusion GPS to conduct a smear campaign against me and Sergei Magnitsky in advance of congressional hearings on the Global Magnitsky Act," Browder testified. "He contacted a number of major newspapers and other publications to spread false information that Sergei Magnitsky was not murdered, was not a whistle-blower and was instead a criminal."

Browder was clear that he believed Russians paid Fusion GPS to conduct the anti-Magnitsky Act campaign. And of course, Fusion GPS was also behind the Trump Dossier. And that left Republican Sen. Lindsey Graham with lots of questions.

"The group that did the dossier on President Trump hired this British spy, wound up getting it to the FBI. You believe they were working for the Russians?"

"In the spring and summer of 2016 they were receiving money indirectly from a senior Russian government official," Browder answered.

"Okay," said Graham. "So, these are the people that were trying to undermine Donald Trump by showing the nefarious ties to Russia, is that what you are saying?"

"Well, what I'm saying with 100 percent certainty is that they were working to undermine the Magnitsky Act and the timing of that," Browder said.

What's important to remember from that exchange is that Browder said "with 100 percent certainty," that Russians financed, or helped finance, the Fusion GPS anti-Magnitsky Act campaign. But Browder could not say who funded the Fusion GPS work on the Trump Dossier.

And that, apparently, piqued the interest of Democratic senators.

"Fusion GPS is a firm that does opposition research for clients," Democratic Sen. Sheldon Whitehouse said. "In your case, they took on Russian interests as a client and the task was to apply pressure and opposition research and so forth, and to try to undo or defeat the Magnitsky Act?"

"That's correct," said Browder.

"With respect to Fusion GPS having commissioned the Steele dossier, do you know who the client was for that particular task?"

"I do not."

"OK, so you have no evidence that the Russians were involved in commissioning that particular document?"

"No."

So Browder could not tie Fusion GPS and the Trump dossier to Russian funding and support. But what heartened Republicans was that Whitehouse asked the question. If Democrats want to know who commissioned and financed the Trump dossier, it might be much easier for the Judiciary Committee to find out.

And not just Whitehouse. Democratic Sen. Richard Durbin also appeared curious about who was behind the dossier.

"The Steele dossier is something I'm trying to understand as it relates to Fusion GPS," Durbin said. "Could you put that in perspective as to their role and what that dossier, why it was created and what the people who created it hoped to achieve?"

Browder answered that he only knew the Steele story from what he read in the press, "so I'm just a bystander on that part of the story."

"What I am absolutely familiar with on a first-hand basis is Fusion GPS and Glenn Simpson's role working on behalf of the Russian government to overturn the Magnitsky Act," Browder continued. "And there I think the steps they took very much compromised their integrity."

"But you're saying you don't know of any connection between Fusion GPS and the actual creation or dissemination or use of the Steele dossier?" Durbin asked.

"I do not," Browder said.

Again, the good news for Republicans was not that Browder could enlighten the committee on the Trump dossier. He couldn't. The good news was the Democrats finally showed some interest in learning how the dossier came into being.

That could be particularly important when Simpson, who has in recent weeks refused to testify before the committee and vowed to assert his Fifth Amendment right against self-incrimination, finally sits down with committee investigators in a private, transcribed interview. Simpson has so far stonewalled all questions about who commissioned and financed the dossier. But Thursday's developments give Republicans some hope they will someday learn the answer.