Former Trump campaign adviser Carter Page reportedly has informed the Senate Intelligence Committee that he will not agree to turn over documents or be interviewed and will assert his Fifth Amendment right to remain silent. What the committee does next may have implications not only for its own inquiry but also for the criminal investigation being conducted by special counsel Robert S. Mueller III.

The committee has conducted closed, voluntary interviews of a number of Trump campaign advisers, including Donald Trump Jr. and Jared Kushner, the president's son-in-law, as part of its probe of possible Russian interference with the 2016 presidential election. Investigators are interested in Page because of reports that he had meetings with high-level Russian officials last year while he was working for the Trump campaign.

In light of Page's reported refusal to cooperate, the committee's logical next step would be to subpoena him. Unlike a request for a voluntary interview, a subpoena would compel Page to appear. If investigators believe Page may be trying to stonewall, a subpoena is the way to call his bluff. There's a chance that Page would agree to testify once he was actually before the committee. In fact, there are some conflicting reports that Page has denied taking the Fifth and would be willing to testify at a public hearing — although perhaps not in a closed session. Regardless, if he's refusing to be interviewed, the best way to join the issue and clarify Page's position is probably to subpoena him to appear before the committee and see what he does.

If Page is subpoenaed and continues to take the Fifth, the committee has several options. It could simply accept the privilege claim and move on with its investigation, trying to gather the necessary information from other witnesses and sources.

If the committee believes the privilege claim is unfounded, it could vote to hold Page in contempt of Congress for refusing to testify. Congress did this in 2014 in the case involving former IRS official Lois Lerner, who took the Fifth before a congressional committee investigating alleged abuses by the Internal Revenue Service.

A citation for contempt of Congress then goes to the U.S. attorney for the District of Columbia for investigation and possible prosecution. But the U.S. attorney is not required to prosecute if the case lacks merit. That's exactly what happened in Lerner's case — the U.S. attorney concluded she had a valid Fifth Amendment claim and that a contempt prosecution would not be appropriate. And of course, a contempt referral and possible related court battles would take many months, during which Page would still be silent.

A third option, and the one loaded with the most potential land mines, is for the committee to immunize Page and compel him to testify. Congress, like the Justice Department, has the statutory power to immunize witnesses. Once immunized, Page would have to testify and anything he said could not be used against him in a criminal case. That might help the committee get to the bottom of what happened in the Russia inquiry. But granting immunity might also jeopardize any potential criminal case against Page that Mueller could be considering.

This happened most famously during the Iran-contra scandal in the 1980s, when the Senate granted immunity to Oliver North and compelled him to testify. North was later prosecuted and convicted, but an appeals court threw out his convictions. The prosecutors could not prove that witnesses at the criminal trial had not been influenced by North's immunized, nationally televised testimony.

Presumably the lessons of the North case would make Congress reluctant to immunize Page and potentially be seen as creating obstacles to Mueller's investigation. If members of Congress did appear headed down that road, Mueller could weigh in and try to persuade them not to proceed. And granting immunity would require a vote of two-thirds of the committee members, which means some Democrats would have to agree. So if Page is angling for immunity, he's probably unlikely to get it from the Senate.

If Mueller is indeed investigating Page, he may ultimately face the same issues now facing the Senate committee. Page presumably would take the Fifth if called to testify before the grand jury. Mueller would then have to decide whether to immunize Page, try to build a case against him without his testimony and possibly persuade him to plead guilty and cooperate, or to just set Page aside and move on.

These issues are common in large criminal investigations, and the more witnesses who invoke the Fifth, the more complicated the decisions become about how to proceed. But so long as Congress does not throw a wrench into the gears, Mueller can deal with recalcitrant witnesses in the ordinary course of his investigation.

Individuals fearing incrimination and taking the Fifth are certainly a further example of the smoke surrounding the events being investigated in the various Russia probes. Whether there is an underlying criminal fire still remains to be seen.