The Iran-Contra scandal offers a cautionary tale for how a Republican-majority Congress could stall the investigation into the Trump campaign's ties to Russia.
The special prosecutor in that investigation of Reagan administration officials asked lawmakers not to grant immunity to witnesses in exchange for their testimony, because he feared it would prevent their prosecutions, reported Politico.
And that's exactly what happened.
Former national security adviser John Poindexter and his deputy, Lt. Col. Oliver North, were granted limited immunity for their congressional testimony about secret arms sales to Iran that were used in part to fund Nicaraguan right-wing militants.
Lawrence Walsh, the former federal judge appointed in 1986 to investigate the case, was embittered as he watched both White House officials' convictions on multiple felonies overturned after appeals courts found their prosecutions had been tainted by their own testimony in congressional hearings.
The lawyer for one of the key figured in the Trump-Russia probe told Politico that, since the appointment of Robert Mueller as special counsel, a number of witnesses connected to the GOP presidential campaign were reconsidering their offers to testify before Congress unless they are granted immunity.
"With the appointment of Mueller, this investigation got a lot more real for everyone," said the lawyer, speaking on the condition of anonymity. "Why would you send clients up to Congress now and let them get caught up in a perjury trap over what could be a minor issue?"
Trump advisers who have offered to cooperate fully with Congress are Jared Kushner, the president's son-in-law and senior adviser, former campaign chairman Paul Manafort, and campaign advisers Roger Stone and Carter Page.
Legal experts expected Mueller, the former FBI director overseeing the Russia probe for the Department of Justice, to ask lawmakers not to grant immunity for testimony -- even if that slows the congressional investigations.
The Republican leaders of House and Senate committees investigating possible election collusion and financial ties to Russia have so far said they don't plan to offer immunity, but the temptation may prove too great.
Lawmakers may decide to grant immunity if they feel pressure to show progress in the investigation, and congressional Republicans have already been accused of helping the White House cover up alleged campaign ties to the Kremlin.
Granting immunity to high-profile targets -- including disgraced national security adviser Mike Flynn, who has reportedly asked for immunity in exchange for his testimony -- could be politically risky, however.
Public testimony would only draw more attention to the scandal consuming the White House, while letting Mueller investigate the allegations quietly and more deliberately could take the political heat off congressional Republicans.
"I think that the Republicans would be happy to let this drag along quietly without them making any news at all," said Alex Whiting, a Harvard Law professor and an expert on criminal prosecutions.
But that tactic could be more dangerous to the president and his campaign advisers -- who could face prosecution without immunity.