While President Donald Trump’s sudden firing of FBI Director James Comey on Tuesday has brought the FBI’s investigation of potential ties between the Trump campaign and the Russian government back into the spotlight, it’s worth remembering that similar investigations are still happening in Congress, in the House and Senate Intelligence Committees.

And in the Senate, at least, things are getting serious: On Wednesday, the committee announced it has issued a subpoena to former National Security Adviser Michael Flynn, demanding he turn over documents related to the investigation.

Committee chair Sen. Richard Burr (R-NC) and ranking member Sen. Mark Warner (D-VA) had previously said that anyone who was asked for documents and didn’t produce them by Tuesday night would be subpoenaed. Flynn (who reportedly asked the committee to guarantee him immunity from prosecution in exchange for his cooperation with the investigation, and wasn’t granted it) didn’t cooperate. So on Wednesday, they demanded he turn over the documents as a matter of law.

While the House investigation into Trump’s Russia ties has become totally derailed by posturing and recriminations, and the FBI investigation is under a pall after Comey’s firing, the Senate investigation appears to be proceeding fairly smoothly, with Burr and Warner cooperating with each other.

In addition to asking for documents from Flynn and other Trump allies, Senate investigators are reportedly turning to the Treasury Department to suss out Trump/Russia ties, as Vox’s Alex Ward wrote Wednesday:

"We've made a request, to FinCEN in the Treasury Department, to make sure, not just for example vis-a-vis the president, but just overall our effort to try to follow the intel no matter where it leads,” Warner told CNN. "You get materials that show if there have been, what level of financial ties between, I mean some of the stuff, some of the Trump-related officials, Trump campaign-related officials and other officials and where those dollars flow — not necessarily from Russia." FinCEN stands for the Financial Crimes Enforcement Network, the arm of the Treasury Department with the hard task of tracking and stopping the illicit use of money, including money laundering, as well as focusing on the financial side of national security issues. Getting FinCEN involved is a big step for those conducting the Russia-Trump team investigations. So far, four people appear to be at the center of it all: 1. Flynn, naturally 2. Paul Manafort, Trump’s former campaign chair, who we already knew worked as a political consultant on behalf of Russian interests 3. Roger Stone, a former Trump adviser who reportedly told Trump to fire Comey, and celebrated the news with a cigar 4. And Carter Page, another former Trump adviser who found the Comey dismissal “encouraging” Again, this seems like a logical step for any thorough investigation to take. That Warner made the ask is not the real story. That Warner felt it was appropriate to ask — because the investigation needed more information — is.

It might not be a coincidence that Burr was one of the Republican senators to react most strongly to the news of Comey’s firing, saying, “I am troubled by the timing and reasoning of Director Comey's termination.”