Department of Justice

Key players: former FBI director Robert S. Mueller III, who was appointed special counsel and took over this investigation, at the request last week by Deputy Attorney General Rod J. Rosenstein. Pressure mounted on Rosenstein to appoint a special counsel after Trump fired FBI Director James Comey and used a memo written by Rosenstein in an early rationale for the dismissal.

Scope: The order written by Rosenstein directs Mueller to investigate “any links and/or coordination between the Russian government and individuals associated with the campaign of President Donald Trump’’ as well as any matters that “may arise directly from the investigation.’’ He can bring criminal charges.

Senate Select Committee on Intelligence

Key players: Chairman Richard Burr, Republican of North Carolina, and Mark Warner, of Virginia, the panel’s top Democrat.

Scope: The panel initially defined its inquiry to include investigating Russia’s attempts to influence the 2016 election, including any links between Trump campaign and Russian officials, as well as Russia hacking of US e-mails. The investigation is expanding to keep up with events and to look into the circumstances surrounding Comey’s firing.

Senate Judiciary Committee

Key players: Republican Chairman Chuck Grassley of Iowa; top Democrat Dianne Feinstein of California; and Republican Lindsey Graham of South Carolina, who chairs a key subcommittee.

Scope: It has primary oversight authority over the Department of Justice in the Senate and has been dipping into the Russia scandal from that watchdog vantage point. Its inquiry has expanded and intensified with events too.

House Permanent Select Committee on Intelligence

Key players: Mike Conaway, a Texas Republican on the panel who is presiding over the investigation, now that the chairman has stepped away from the probe; Democratic Ranking Member Adam Schiff of California.

Scope: Similar to the Senate Intelligence Committee.

House Oversight and Government Reform

Key players: Jason Chaffetz, Republican of Utah, though he says he will step down from Congress next month; reports are that South Carolina Republican Trey Gowdy will take over the chairman’s seat; Elijah Cummings of Maryland, the top Democrat on the panel.

Scope: This panel has two relatively narrow slices. Early in the year, the committee started looking into payments Michael Flynn accepted for speeches he gave in Russia and lobbying he did on Turkey’s behalf before he was named national security adviser. More recently, the panel is looking into Comey’s firing and the content of his memos.

VICTORIA McGRANE

Victoria McGrane can be reached at victoria.mcgrane@globe.com. Follow her on Twitter @vgmac.