Open hearing, let the country hear him take the 5th on every single question under oath. If he doesn’t show, charge him with contempt. And do it!
It does not say he has a "constitutional rights not to testify under the First and Fifth Amendments of the Constitution.
Get him to testify and plead the Fifth to every single question. Let him show the world exactly who he is.
Bank records showed that Glenn Simpson’s firm was paid by the Democrat National Committee and the Hillary Clinton campaign through the law firm Perkins Coie. Didn’t President Obama say his was the most transparent administration ever? Wasn’t President Obama the titular head of the Democrat Party in 2016? Glenn Simpson needs to testify in public, under oath. If he wants to take the fifth, let’s hear him do just that.
Who, besides himself, Fusion GPS, his associates, and his paymasters is Glenn Simpson protecting? Fascinating.
And compel him to speak the magic words himself. Don't let him weasel out by using his lawyer for that.