The president suggested he could be investigated for obstruction of justice as part of the Russia investigation because he was "fighting back" and reiterated there was "no collusion" between his campaign and Moscow.
"Oh, well, 'Did he fight back?' " Trump said, "You fight back, 'Oh, it's obstruction.' "
Mueller's team has told Trump's lawyers in recent days they want to question the president about the firing of national security adviser Michael Flynn and FBI Director James B. Comey. They have also asked witnesses in recent weeks about whether Trump has tried to oust Attorney General Jeff Sessions, whom he has publicly criticized.
The president suggested the interview could take place in the next two or three weeks and said he continued to consult with his lawyers. Trump has previously criticized the wide-ranging investigation into his administration, calling it a "hoax" and a "witch hunt," while alternatively saying he would probably testify or that he may not need to testify.
On Wednesday, Trump also sought to contrast himself with his former Democratic foe, Hillary Clinton, who was questioned by the FBI in July 2016 in connection with the probe into her use of a private email server as secretary of state.
"She didn't do it under oath, but I would do it under oath,'' he said.
Republicans have repeatedly suggested that the FBI went easy on Clinton in her questioning in part because she was not under oath for that interview. But FBI interviews are typically not conducted under oath, and it is still a crime to lie to an FBI agent. Clinton could have faced criminal charges if investigators had concluded she had lied to them.
The comments came during an impromptu meeting in the West Wing, where reporters were gathered to speak with senior officials for a background briefing about immigration. Trump walked into the meeting unannounced and began talking. The president later told reporters to quote him on the record.
Trump's remarks took White House officials by surprise and came as his lawyers were negotiating with Mueller's team on a potential interview. The president's lawyers have repeatedly encouraged him not to post tweets or make comments about the investigation without their knowledge, saying such comments could damage him.
The president's statements suggest that he sees an obstruction-of-justice investigation as an unfair attack on attempts by him or others to mount a defense. It is not a crime for the subject of a criminal probe to assert their innocence or provide additional information to exonerate themselves. However, if a person takes steps to impede or stop such an investigation, that can amount to obstruction of justice.
"Obstruction is trying to avoid the investigation, taking overt acts to avoid the truth or avoid the investigation's progress,'' said Barbara Van Gelder, a white-collar defense lawyer. "I think he's just taking a layperson's view of obstruction. An off-the-cuff remark, by anyone, even the president, in response to a shouted question really shouldn't be taken as gospel," she said.
People who have appeared before Mueller's team say prosecutors have detailed accounts of events, sometimes to the minute, and have surprised witnesses by showing them emails or documents they were unaware that the team had or that their colleagues had written. One person said Mueller's team has asked about Trump's private comments around key events and how he explained decisions.
"They are looking for a pattern," said this person, who has spoken with Mueller's team and requested anonymity to speak about a federal investigation.
Among Trump's friends, there is a prevailing view that he could damage himself by testifying under oath because he often misrepresents events and that he is listening to lawyers who are not giving him good advice.
"He should treat Mueller like a plague," Chris Ruddy, the CEO of Newsmax and a Trump confidant, said Wednesday after Trump's remarks. "He should assert executive privilege in every opportunity they can."
Ruddy said Mueller's investigation isn't about "Russian collusion."
"It's about anything and everything they can find," he said. "This is moving rapidly, extremely fast."
Even as the president agreed to testify, he continued to raise questions about the FBI and Mueller's investigation, saying that missing text messages between two senior officials involved in the Clinton and Trump investigations raised concerns.
Trump also said he didn't recall asking acting FBI director Andrew McCabe whom he voted for in an Oval Office discussion earlier this year, as The Washington Post reported Tuesday. The conversation left former and current FBI officials concerned because they believed it was inappropriate for the president to ask a civil servant about his political leanings. McCabe replaced Comey as head of the FBI until Christopher A. Wray was confirmed for the job in August.
"I don't think I did," he said. "I don't know what's the big deal with that. I would ask you who you voted for. . . . I don't remember asking him that question."
"I think it's also a very unimportant question," he added.
Trump also lambasted McCabe's wife for taking political donations from a group tied to Hillary Clinton during her bid for a Virginia state Senate seat, The Post reported. Trump reprised those criticisms during Wednesday's quick session with reporters.
"McCabe got more than $500,000, essentially, from Hillary Clinton," Trump said. In fact, McCabe's wife took donations from a political group run by a Clinton ally.
Asked if he thought Mueller would treat him fairly, Trump said, "We're going to find out.''
The president has been frustrated with news coverage about whether he would testify in front of Mueller and insists that he has done nothing wrong, according to a Trump adviser who requested anonymity to talk about Trump's deliberations.
This person said Trump is frustrated that the investigation is no longer about Russia but is convinced it would be too dangerous to try to move against Mueller or any other Justice Department officials, at least for now.