Republicans in Congress took several steps this week toward investigating President Trump’s campaign and administrative ties to Russia. Those steps still fall short of the most aggressive probes Congress can launch, but they have helped satisfy at least some of the Democrats who for months have accused GOP lawmakers of shielding Trump from scrutiny on a widening controversy.

Congressional Democrats are continuing to call for Republicans to do more — a reflection of both the politics at play and the complicated degrees of investigative power that Congress can deploy on a given issue.

Understanding those powers — the different steps congressional committees can take to investigate a president — is critical to understanding the political fight around them.

Quick context: Last week, the Washington Post revealed that Trump National Security Adviser Michael Flynn had spoken with the Russian ambassador about sanctions during President Obama’s time in office. Flynn later resigned after it became clear he had misled Vice President Mike Pence about his dealings with the Russian envoy.

The ensuring uproar has spurred Senate Republicans — who had seemed to be dithering on a Russia probe — to concrete action. Sen. Richard Burr (R-NC), the chair of the Intelligence Committee, said Wednesday that he will “very likely” invite Flynn to testify. Democratic staffers on that committee privately say that the Intelligence Committee is now proceeding on a bipartisan basis, according to BuzzFeed.

On Thursday, Sen. Chuck Grassley (R-IA) joined Sen. Dianne Feinstein (D-CA) in a bipartisan letter demanding the FBI deliver a briefing on “the circumstances that led to the recent resignation” of Flynn, as well as copies of the transcripts of his conversations with Russian officials.

“It so obvious to the public that something’s happening here that they do have to start taking steps,” says Michele Swers, a congressional expert at Georgetown University, about Senate Republicans. “Earlier, Burr was not interested, and you didn’t see any urgency to investigate Russian election hacking. But when you have Flynn stepping down and people from intelligence committees leaking evidence, he’s moving in the direction of, ‘Okay, this really is worth investigating.’”

Still, many Democrats are demanding even more aggressive investigations. House Democrats in particular, as well as some national security experts, have called for a bipartisan, independent “select committee” investigation, which Republicans have thus far resisted.

The multiple kinds of investigations

Before we get to the politics of this debate, it’s useful to lay out the different kinds of potential investigations into Trump and Russia.

First, there are what are known as standing committee investigations. The Senate and House have dozens of committees with their own separate policy fiefdoms — part of their mandates involve looking into problems in the executive branch related to their areas of expertise.

When news of Russian election hacking first began gathering steam last summer, a whole bunch of standing committees — including the Senate Armed Services Committee and the Senate Foreign Relations Committee — held hearings, citing their jurisdiction to investigate. But, gradually, the Intelligence Committee has taken the lead on the Russia probe. That’s because that committee has the widest authority to look into all of the executive branch’s intelligence agencies over this particular probe, according to Swers.

Dozens of congressional Democrats have called for the formation of what would almost certainly be a more aggressive investigative vehicle: a bipartisan select committee. The standing committees give Republicans full control over all subpoenas that get issued, which witnesses (if any) are compelled to testify, and which records have to be preserved during the investigation. (Though the Intelligence Committee rules does allow the Vice Chairman and other members to issue subpoenas.) By contrast, the bipartisan select committee would evenly distribute those powers to members of both parties.

Moreover, unlike the standing committees, the select committee would be exclusively devoted to investigating this one issue — freeing up manpower and personnel that the standing committees don’t have. And the select committee would be much more likely to hold hearings in public and be more transparent about the results of its findings than the Intelligence Committee, which is known for its secrecy, according to Swers.

“This is an important enough committee to solely focus on this one issue,” said Rep. Tim Ryan (D-OH) in an interview this fall. “If it’s just led by the Armed Services Committee, they have a lot of other things going on — the day to day where they’ll be dealing with Syria and Aleppo and Turkey. [The select committee] would move it out of that atmosphere.”

Confusingly, there’s another kind of bipartisan investigation that some have called for: the independent commission. This would be like the select committee in that its members would be exclusively charged with investigating one question, and in that it would be controlled in a bipartisan fashion.

But unlike the select committee, the independent commission would operate on a much longer time horizon and be tasked with producing a formal report that would offer solutions for how to prevent foreign hacking in future elections. (Think the 9/11 commission.)

The last kind of investigation some Democrats are calling for would be led by the executive branch: a special prosecutor. There’s no word on what he’ll do yet, but Attorney General Jeff Sessions — a close Trump ally — is viewed by Democrats as too political a figure to lead a Justice Department investigation into Trump. (Among the most famous examples of special prosecutors are Archibald Cox, who was appointed by President Richard Nixon’s attorney general to investigate Watergate, and Robert Fiske, who was chosen to probe Bill Clinton’s Whitewater scandal in the 1990s.)

The uneven partisan breakdown of the investigation fight

It’s been easy for the press to characterize the fight over the investigation as a partisan squabble — with Democrats calling for the independent probe and Republicans backing the standing committees, which they control.

But the actual party-line breakdown is more complicated.

In part, that’s because some Democrats on the relevant standing committees have said their bodies are equipped to conduct the investigation. The two most prominent Democrats on the Senate Intelligence Committee — Feinstein, who served as its chair and remains on of its senior members, and Sen. Mark Warner (D-VA), now the committee’s top-ranking Democrat — have both backed congressional Republicans’ plan. That puts them at odds with House Democrats, who have stepped up their calls for an independent commission this week, as well as some Senate Democrats.

It's time for a select bipartisan committee on the involvement of Russia in this administration and election. Period. Stop. Public hearings. — Claire McCaskill (@clairecmc) February 14, 2017

“I think it’s fair to say there are differences of opinion in the caucus,” Feinstein said after the Democratic meeting on Thursday, according to the Washington Post.

For now, Warner and Feinstein have the support of key party leadership. Minority Leader Chuck Schumer has backed off his earlier calls for an select committee, backing the standing committees while also insisting that they must work in a “bipartisan” manner.

Further complicating matters is the fact that at least two Senate Republicans have suggested they don’t think the standing committee process is enough. In December 2016, Sens. John McCain and Lindsey Graham — two vocal Trump critics and Russia hawks — both called for the bipartisan independent committees to investigate Trump. Since then, both have also backed off that push, citing a lack of “support” in the rest of the Senate body, according to the Washington Post.

House Republicans have shown significantly less appetite for an independent, bipartisan probe than their colleagues in the Senate. “There is not going to be one; I can tell you there is absolutely not going to be one,” House Intelligence Committee Chair Devin Nunes told Politico.

Are the standing committees going far enough?

So it looks, for now, almost certain that the standing committees will bear the weight of the Russia investigation. It’s hard to know if they’re up to the task, in part because it’s hard for the public to know exactly what they are or aren’t doing.

Burr has promised that an investigation will span from the “post-election period to the year leading up to the election,” and said executive branch officials may be called to testify, according to BuzzFeed. He also told Politico that committee staff had begun reviewing reviewing documents for its Russia probe last week, and that it’s “very likely” Flynn will be called to testify.

Still, no hearings have been scheduled. And Democrats remain concerned that their Republican colleagues are reacting to the uproar in the media over the Flynn allegations but that their interest in pursuing the investigation will wane once the intensity dies down.

In response, there are three things in particular that Schumer says his caucus is “united” in believing the congressional investigations must provide to probe Trump’s Russia ties:

Preservation of relevant records: Senate Democrats are calling for the Trump administration to be legally compelled to preserve all records, including texts and emails, related to potential ties to Russia.

Senate Democrats are calling for the Trump administration to be legally compelled to preserve all records, including texts and emails, related to potential ties to Russia. Public testimony from administration officials: “It’s been reported that campaign officials have had constant contact with Russian intelligence officials. They must testify,” Schumer said in a speech on the floor on Thursday. (Matt Yglesias has more on that here.)

“It’s been reported that campaign officials have had constant contact with Russian intelligence officials. They must testify,” Schumer said in a speech on the floor on Thursday. (Matt Yglesias has more on that here.) Sessions’s recusal: Schumer has also demanded that Attorney General Sessions, a close Trump backer and advocate during the campaign, “recuse himself this matter immediately.” According to congressional Democrats, the Department of Justice should decide how it wants to investigate Russia’s ties to Trump without Sessions’s input.

Senior Democrats say they’ll revive calls for an independent commission should the Intelligence Committee not move swiftly enough or comply with their three key requests. “If at any point we are not able to get the full information and we’re not pursuing the information to where the intelligence leads, we’ll look at other options,” Warner told the Washington Post.

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