Trump attacks Mueller after he agrees to testify to Congress
WATCH: The president responded to questions about Robert Mueller's plans to testify in front of Congress.

President Donald Trump on Wednesday attacked Robert Mueller hours after word came that the former special counsel had agreed to testify before Congress in public on July 17.

Trump once again labeled Mueller's investigation a "witch hunt" and a "hoax" and accused him of illegally handling the derogatory text messages exchanged between former FBI agent Peter Strzok and former FBI lawyer Lisa Page, saying Mueller had "terminated" the messages, calling that "illegal."

"That's a crime," Trump said in an interview with Fox Business Network anchor Maria Bartiromo.

President Donald Trump awaits the arrival of Canadian Prime Minister Justin Trudeau to the White House on June 20, 2019, in Washington.

Trump has argued the point before in attacking Mueller, including in a tweet dating back to December 2018.

Special counsel Robert Mueller speaks at the Department of Justice, May 29, 2019, in Washington, DC, about the Russia investigation.

Mueller was "obviously not a Trump fan," the president said.

President Donald Trump talks to reporters as he departs for travel to the G20 Summit in Osaka, Japan outside the White House, June 26, 2019.

Later Wednesday, as he left the White House for the G20 summit in Japan, Trump once again lashed out at Mueller agreeing to Democrats' demands he testify .

"There was no collusion, no obstruction, no nothing. How many times do have to hear it? It never ends. He keeps going on and on. I've been going through this for two and a half years. The criminal activity was on the other side. With the fake dossier, the phony fraudulent dossier, and all the other things ... this is a disgraceful thing," he told reporters.

"I heard about it last night, and I just said, "Does it ever end? At what point does it end?" It's a disgrace. No obstruction, no collusion," Trump said.

ABC News' Chief Washington Correspondent Terry Moran asked the president if he would try to block Mueller from testifying.

"I don't know anything about it, I just heard," Trump responded. "And my only response to Mueller is, does it ever stop? After all of these years, time and people, does it ever stop? And the Democrats use it to try and divert from what they have, because what they've done -- if you look and you see, and it's just my opinion, tremendous criminal activity on their side. And they know it, and this is the diversion. But I ask you this -- does it ever stop?"