While Trump's team is focused on the implications this ruling will have on the Jan. 6 case, they are also particularly interested in how this could affect his other outstanding criminal cases.

Why's that?

Trump's lawyers have an outstanding motion to dismiss the Florida classified documents case based on presidential immunity.

While it's not likely that case will go to trial before the election, the judge in that case, Judge Aileen Cannon, has indicated she wants to wait for the Supreme Court decision before she entertains that motion. And, given her unpredictability, the Trump legal team believes the ruling could give Cannon yet another avenue to throw the case's future in doubt.

The best case scenario for Trump's lawyers would be for the Supreme Court to rule he has full immunity for any actions taken while in office, which is not likely. The worst case would be that the justices uphold lower court rulings that said criminal laws apply to ex-presidents like they apply to everyone.

What do they expect? Not a full win for either side.

If the Supreme Court says its mandate could go into effect immediately, Trump's lawyers expect Judge Tanya Chutkan to get the ball rolling very soon after in the Jan. 6 case and likely schedule a briefing in the next week and a status conference once the mandate is docketed.

There would also likely be action in Florida, where Judge Cannon could move to schedule a briefing or an in-person hearing on the motion to dismiss.

-ABC News' Katherine Faulders

When the justices appeared open to the idea of some level of immunity for former presidents, it was a shock for many veteran court observers.

"It was surprising to hear, at least from some of the justices, the possibility that a president could somehow commit criminal misconduct for which they could never be held liable in court," said constitutional law expert Michael Gerhardt. "I think that has struck many people as just, up until now, inconceivable."

One point that stood out to Gerhardt was when Justice Elena Kagan pressed Trump attorney John Sauer if a president could order the military to stage a coup and be immune. Sauer said, in their view, a president could.

"The answer that she got was one of the most disturbing I've ever heard at the Supreme Court," he said.

Read more about reaction to the April arguments here.

The high court in April heard historic arguments on whether former President Donald Trump can be criminally prosecuted related to his efforts to overturn his 2020 election loss.

Trump denies all wrongdoing and insists he should have "absolute immunity" for any "official acts" while in office.

Read the five takeaways from arguments this past April.

The Supreme Court is expected to convene at 10 a.m. today.

Shortly after the Supreme Court ruled Monday on Trump's immunity case, the Biden reelection campaign organized a group of surrogates on a press call to lambast the decision that makes the former president immune from federal prosecution for official actions he took while in office.

The group included Capitol police officer Harry Dunn, New York Rep. Dan Goldman and Texas Rep. Jasmine Crockett. The group criticized the Republican-majority Supreme Court for giving the former president "untethered political power," or freedom to act as a "dictator."

"I do think that it was extremely scary," said principal deputy campaign manager Quentin Fulks, who led the call. "So what happens if there's an election outcome [or] result that Trump doesn't like in a Senate race, or governor's race or House race?"

The campaign said that Biden would be out on the campaign trail to highlight the threat that Trump poses to democracy following this decision.

"The Supreme Court just handed Donald Trump three keys to absolute immunity as president of the United States and so we're going to continue to point out to voters," Fulks said. "When Trump says these things, now he will have the ability to do them if he is the president or reelected president of the United States, and we have to do everything in our power to stop."

Fulks diverted attention from a question about Biden's debate performance, saying the Supreme Court's decision was a "reality check" in the face of debate night.

"Now until November, we're going to continue taking this case directly to voters who are going to decide this election," he said.

-ABC News' Isabella Murray