by DARTUNORRO CLARK, KATY TUR and ALEX JOHNSON

After a day spent belligerently defying special counsel Robert Mueller, former Donald Trump campaign aide Sam Nunberg appeared to reverse himself Monday night and said he likely will cooperate with a subpoena seeking campaign documents related to the Russia investigation.

Nunberg helped Trump prepare for the first Republican presidential primary debate in August 2015 along with the man he has described as his mentor, veteran Republican operative Roger Stone. He made a bravado tour of television talk shows Monday declaring he wouldn't cooperate with the subpoena.

"The president's right, it's a witch hunt," Nunberg told MSNBC's Katy's Tur.

But Monday night, Nunberg, who said he still hadn't talked with his attorney, told NBC News that he would probably cooperate with Mueller in the end. He said he objected to the subpoena because it asks for information about people whom he either never talked to or with whom he had close relationships.

"I just don't want to make it easy," he said. "I don't think it's fair to ask for my personal communications."

The special counsel's office had no comment.

In his interview with Tur, Nunberg said he was distressed that Mueller's team would "insinuate that Roger Stone was colluding with [Wikileaks founder] Julian Assange."

According to the subpoena, which was sent to Nunberg by Mueller, investigators want emails, text messages, work papers, telephone logs and other documents going back to Nov. 1, 2015, 4½ months after Trump launched his campaign.

Nunberg, who has already been interviewed by Mueller's office, said the idea that Trump or his campaign colluded with Russia was the "biggest joke," but he suggested — without any evidence — that Mueller may have something on the president.

"I think they may," Nunberg said. "I think that he [Trump] may have done something during the election. But I don't know that for sure." He didn't provide any details.

Nunberg also said Mueller's investigators have asked him a wide range of questions about a meetingamong Donald Trump Jr., Paul Manafort, Jared Kushner and a Russian lawyer in Trump Tower in June 2016, including whether he heard anyone speaking Russian in Trump's office and why Trump took favorable positions toward Moscow during the campaign.

White House Press Secretary Sarah Huckabee Sanders blasted Nunberg on Monday and rebutted any suggestion that the campaign colluded with Russia.

"I definitely think he doesn't know that for sure, because he's incorrect," she said. "He hasn't worked at the White House, so I can't speak to him or the lack of knowledge he clearly has. As we've said many times before, there's been no collusion."

Nunberg later told CNN that he believed Trump knew about the Trump Tower meeting with the Russian lawyer. The president has denied that he knew about the meeting.

"He talked about it for a week before, and I don't know why he did this. All he had to say was: 'Yeah, we met with the Russians. The Russians offered us something, and we thought they had something.' And that was it. I don't know why he went around trying to hide it when he shouldn't have," Nunberg said.

The Trump campaign fired Nunberg later in August 2015 after racially charged statements were uncovered on his personal Facebook page, a campaign spokesman said at the time. He denied having written the posts.

The Trump campaign went to court in July 2016, accusing Nunberg of having leaked potentially damaging information to the media. The case was settled later that year.

What are Nunberg's options?

Anyone subpoenaed to testify before a grand jury has the right to refuse to answer questions to avoid self-incrimination. The government can grant immunity to get the witness to testify, but the witness can no longer refuse to answer questions and can't be prosecuted for information he or she provides.

A witness can also ask a judge to quash the subpoena on the ground that compliance would be "unreasonable or oppressive," but such motions are seldom granted.

Witnesses who simply refuse to appear before a grand jury or who won't answer questions, without asserting their Fifth Amendment rights, can be held in contempt of court and put in jail until they agree to answer or until the term of the grand jury expires, whichever comes first.

Nunberg said he wasn't fearful of what Mueller may think of his refusal to cooperate or the possibility of being arrested.

"I think it would be really, really funny if they wanted to arrest me," he said. "Let them think what they want. It's absolutely ridiculous what they want from me."