From the LA Times in 2017:
Trump could pay a price if he hands out pardons in the Russia probe as he did for Joe Arpaio
By DAVID G. SAVAGE
LA Times STAFF WRITER
AUG. 31, 2017
Excerpt...
But when charges or potential charges are wiped away by a presidential decree, so too is the right to refuse to testify before a grand jury or before Congress about what they know.
As the Supreme Court put it in 1895, If the witness has already received a pardon, he cannot longer set up his privilege, since he stands with respect to the offense as if it had never been committed, said University of Texas law professor Steve Vladeck.
Of course, that only works for federal offenses, Vladeck said. The president cant pardon offenses against state law, and so theoretically, someone like Flynn or Manafort could still argue that they have a 5th Amendment right based upon potential state law crimes. That would, no doubt, provoke some pretty major litigation.
Still, the conflict between the presidents pardon power and a defendants right to remain silent could complicate any White House effort to thwart the investigation. Moreover, Trump could build a case of obstruction of justice against himself if he pardoned close associates who were under investigation.
Continues...
https://www.latimes.com/politics/la-na-pol-pardon-legal-trump-20170831-story.html
So long, Dumpy.