The U.S. Supreme Court in July handed down what one justice called a "rule for the ages" on presidential immunity.

But the dismissal of special counsel Jack Smith's federal election subversion case against Donald Trump leaves key questions about the extent of executive power unanswered.

Smith's criminal prosecution was set to be the first major test of the court's blockbuster decision, in which the conservative majority held former presidents are entitled to absolute immunity for "core" constitutional functions and presumptive immunity for "official" acts but no immunity for "unofficial" acts.

What constituted an official or unofficial act raised "difficult questions" said Chief Justice John Roberts, and was largely left to lower courts to parse out answers through hearings and appeals about specific facts and actions.

Could Trump be held liable for alleged pressure on then-Vice President Mike Pence to unilaterally reject the 2020 election outcome? What about his false statements to the public about voter fraud?

That's impossible to say for now as Smith moved to have the case dropped in the wake of Trump's 2024 win, citing long-standing Justice Department policy barring the prosecution of a sitting president. He also dropped the classified documents case against Trump.

"This uncertainty over the scope of presidential immunity raises the specter for both Trump and any future president that they truly are above criminal law," said David Schultz, a professor of political science and legal studies at Hamline University in Minnesota.

Trump is already entering office with fewer potential checks than in his first term. Both the House and the Senate will be controlled by Republicans, making congressional oversight and impeachment two tools unlikely to be used should he be accused of crossing a traditional boundary.

He will also not be subject to electoral accountability, given that this is the last term he can serve.

The possibility of criminal prosecution would normally be another check, but experts aren't so sure after the Supreme Court's decision.

Michael Gerhardt, a constitutional law professor at the University of North Carolina, said the immunity ruling "will undoubtedly ensure that there will be very few, quite limited guardrails against any abuse of power."

"To the extent that one is concerned about that emboldening him to take action without regard to consequences of criminal prosecution, that's a real concern," said Jessica Roth, a professor at Cardozo School of Law and a former federal prosecutor.

The Supreme Court's liberal justices raised similar fears in their dissents, but Chief Justice Roberts pushed back that the majority opinion "does not place him above the law."

"Like everyone else, the President is subject to prosecution in his unofficial capacity," he wrote. "But unlike anyone else, the President is a branch of government, and the Constitution vests in him sweeping powers and duties."

U.S. District Court Judge Tanya Chutkan tossed the federal election subversion case without prejudice, meaning, in theory, the charges could be filed again when Trump leaves office. Though experts noted such a scenario is highly improbable and could run up against statute of limitations or other problems.

Some immunity questions could still play out in the state cases against Trump in New York and Georgia -- but those have also stalled in recent weeks.

Trump was convicted by a jury on 34 felony charges in connection to a hush money payments made just before the 2016 election. Now, he's seeking to have the case dismissed based on the U.S. Supreme Court's immunity ruling. The judge has indefinitely postponed sentencing for Trump until the issue is sorted.

"That's the place where we'd see the Supreme Court decision tested most immediately," said Norm Eisen, a senior fellow at the Brookings Institution who served as special counsel to the House Judiciary Committee during Trump's first impeachment trial.

Still, Eisen said "we will not get all the answers in the state case because it's a pretty tangential immunity claim."

Eisen noted ongoing prosecutions against other figures involved in efforts to overturn the 2020 election could keep at least some of Trump's past behavior in the spotlight.

"[Trump] may be immune, he may be in office, but all over the country cases have been brought against the false electors," Eisen said. "And those cases will proceed to trial and illuminate Trump's involvement even though he's not a defendant in those cases. That's another place where certainly there's going to be a form of public narrative about what happened, his role in it and whether he should be held accountable."