With Trump subpoena likely this week, what's next for the Jan. 6 committee?

In a dramatic end to what might be its last public hearing, the Jan. 6 committee took the historic step to vote to subpoena Donald Trump.

The subpoena will likely be formally issued this week.

On Thursday, all nine members of the panel approved the resolution to compel the former president to testify about the Capitol attack, which the committee argues was the violent culmination of Trump's many efforts to overturn the 2020 election.

"He must be accountable," chairman Bennie Thompson, D-Miss., said before the vote. "He is required to answer for his actions."

There's been discussion among committee members and staff for months about whether they would want Trump to testify in a live setting. There's no doubt they want him to testify under oath, as committee members made clear in the hearing.

Some members are hesitant to give Trump a live stage, while others view it as beneficial to their investigation as they would get to question him under oath. And there appears to be more of an openness among committee members to have him appear live.

Trump has told advisers he'd welcome a live appearance, according to sources familiar with his thinking, but has yet to say publicly whether he'll cooperate.

The committee would need to negotiate with Trump if he were to offer to testify live in response to the panel's subpoena, Rep. Adam Kinzinger said Sunday.

"I think that's going to be a negotiation," Kinzinger, R-Ill., a member of the committee, told ABC "This Week" anchor George Stephanopoulos. "I'll only address that when we know for sure whether or not the president has tried to push to come in and talk to us live."

"He's made it clear he has nothing to hide, [that's] what he said. So he should come in on the day we asked him to come in. If he pushes off beyond that, we'll figure out what to do next," Kinzinger said.

Trump did not answer whether he would appear in a 14-page memo sent to Thompson Friday, in which he continued his attacks on the panel and continued to make false claims about the presidential race.

"This memo is being written to express our anger, disappointment, and complaint that with all of the hundreds of millions of dollars spent on what many consider to be a Charade and Witch Hunt," he wrote.

Some experts are wary the public will ever see Trump testify before the Jan. 6 committee.

"Before Donald Trump comes to answer questions about this under oath not only will pigs fly but they will circumvent the globe," attorney Jeff Robins told ABC News Live anchor Linsey Davis.

What if he doesn't cooperate?

If Trump refuses to cooperate, the committee could move to have the full House hold him in contempt and refer the matter to the Justice Department for prosecution.

"If they're not going to do that, then it is essentially symbolic," Nick Akerman, a former Watergate special prosecutor, told ABC News.

Chairman Thompson wouldn't say when asked after the hearing how the committee planned to handle any eventual litigation or defiance of their subpoena.

The House has referred four people to the Justice Department after votes to hold them in contempt -- former Trump White House chief of staff, Mark Meadows, Trump's former social media director Dan Scavino, former Trump White House trade adviser Peter Navarro and form political adviser Steve Bannon. DOJ declined to press charges against Meadows and Scavino. Bannon was found guilty in July for defying the Jan. 6 committee subpoena. Navarro was also indicted on contempt of Congress charges and is scheduled to go to trial next month.

Trump could also attempt to run out the clock by fighting the subpoena if the committee took it to court, as he's done with other investigations and records requests he's faced over the years.

"There are myriad legal and separation of powers issues raised by the subpoena, including whether a congressional committee can compel the president to appear as well as the procedural hurdles in attempting to enforce a subpoena in court which previous court decisions have cast serious doubt upon," Stanley Brand, a former counsel to the House of Representatives who has represented some of the Jan. 6 witnesses, including Scavino, told ABC News.

"There is also a question of timing given the substantial delays in litigating such a subpoena," Brand said, pointing to congressional efforts to subpoena testimony from former White House counsel Don McGahn. The case stretched out in court for nearly two years, and ended with a voluntary agreement by McGahn to testify.

Brand said this issue, if litigated, could take just as long.

Republicans, if they win back control of the House this midterm election cycle as expected, are expected to drop the Jan. 6 investigation and turn to other matters. Top Republicans have already promised investigations into Biden and his son, Hunter Biden.

"Time is not on their side," Akerman said, "considering it's mid-October and there's going to be a new Congress coming in Jan. 1, and there's no guarantee it's going to be controlled by the Democrats."