Transcript for Democratic Sen. Mark Warner defends Robert Mueller investigation
To the developing headline late today on capitol hill, the warning from the senate floral involving the president and any talk of firing Robert Mueller. The top Democrat on the senate intelligence committee issuing a strong defense of special counsel Robert Mueller against critics trying to shut down the Russia investigation. After recently being questioned for nine hours, Donald Trump Jr. Now suggesting there is a conspiracy against his father. Here's ABC's senior justice correspondent Pierre Thomas on that tonight. Reporter: Tonight, that warning from the top democratic senator investigating allegations of Russian collusion. Firing Mr. Mueller or any other of the top brass involved in this investigation would not only call into question this administration's commitment to the truth, but also to our most basic concept, rule of law. Reporter: Warner responding to mounting criticism of special counsel rob Mueller from some congressional Republicans. I call on my Republican colleagues to join me in calling for the firing of Bob Mueller. And look, it's time for Mueller to put up or shut up. Reporter: President trump asked this week if he's considering firing Mueller. No, I'm not. No. What else? What, are you surprised? Reporter: But on Tuesday, just days after Donald Trump Jr. Spent more than nine hours behind closed doors with congressional investigators, the president's son openly talking about a conspiracy against his father. There is, and there are, people at the highest levels of government that don't want to let America be America. Pierre Thomas with us live tonight from Washington. And Pierre, we heard president trump say he's not firing Mueller. So, how does senator Warner explain his concern there late today on the senate floor? Reporter: David, senator Warner says the president's track record is his concern. He points out his colleagues did not expect the president to fire former FBI director James Comey, either. David? Pierre Thomas with us tonight.
This transcript has been automatically generated and may not be 100% accurate.