Transcript for Recent tweets reignite questions about whether Trump will fire Mueller

And good evening. Thanks for joining us on this Sunday. I'm Tom llamas. We begin tonight with president trump, and his most direct attack on special counsel Robert Mueller yet. The president on Twitter, sparing no one close to the Russia investigation. Unloading especially on Mueller. Insisting the special counsel is running a partisan witch hunt. Also blasting Andrew Mccabe, a firing trump's attorney used to insist the investigation should be shut down. The attacks re-igniting questions about whether trump will fire Mueller. Here's Tara Palmieri. Reporter: Tonight, president trump escalating his attack. Now targeting the very top of the Russia investigation. Tweeting his strongest rebuke yet at special counsel Robert Mueller. "The Mueller probe should never have been started in that there was no collusion, and there was no crime, witch hunt!" The Russia story is a total fabrication. I call it the Russian hoax. The entire thing has been a witch hunt, and there is no collusion. Reporter: Trump has consistently undermined the investigation, but this latest direct shot at Mueller comes as his lead attorney is calling for the case to be shut down. Lawmakers on both sides of the aisle warning trump that firing Mueller will have severe consequences. If he tried to do that, that would be the beginning of the end of his presidency because we're a rule of law nation. This would undoubtedly result in a constitutional crisis, and I think Democrats and Republicans need to speak out about this right now. Reporter: Tonight, Mueller's team combing through new evidence. A source telling ABC news fired FBI deputy director Andrew Mccabe has been interviewed by investigators, and handed over memos detailing his interactions with trump. You cannot stop the men and women of the FBI from doing the right thing, protecting the American people, and upholding the constitution. Reporter: Mccabe was axed ahead of an inspector general report that accuses him of leaking, and then not being truthful when asked about it. He has denied wrongdoing. He says he's been singled out in the aftermath of FBI director James Comey's firing. Trump blasting Mccabe and his memos with a tweet, "Spent very little time with Andrew Mccabe, but he never took notes when he was with me. I don't believe he made memos except to help his own agenda, probably at a later date, same with lying James Comey. Can we call them fake memos?" Republicans now urging trump to show restraint as his frustration nears a boiling point. If you've done nothing wrong, you should want the investigation to be as fulsome and thorough as possible. Let's bring in Tara Palmieri. President trump tweeted that Mueller's team is biased politically. But that wasn't exactly correct? Reporter: That's right, Tom. President trump tweeted, why does the Mueller team have 13 Democrats and zero Republicans? We checked. 13 of the investigators are registered as Democrats, but four are unaffiliated with either party. The leader of the investigation was registered as a Republican. Tom?

This transcript has been automatically generated and may not be 100% accurate.