[Signalman]

Make him testify, under oath. See if he’s willing to commit perjury. He’ll probably plead the 5th though, if he’s formally charged with a criminal offense.

[tanknetter]

Make him testify, under oath. See if he’s willing to commit perjury. He’ll probably plead the 5th though, if he’s formally charged with a criminal offense.

Can't do that, the National Security Advisor is not a Senate-confirmed position, so is covered under Executive Privilege. There's a long history, spanning both Democrat and Republican administrations of going to every possible length to prevent the NSA from testifying before Congress, particularly in what are deemed to be adversarial situations. When it does happen, the White House makes sure to note that the testimony is being provided voluntarily, and is done under very strict questioning guidelines.