• Supreme Court Justices Sonia Sotomayor, Ketanji Brown Jackson and Elena Kagan laid out grim visions of U.S. democracy in their written dissents to the court's decision on Donald Trump's presidential immunity.
• A University of Chicago legal historian said their written opinions were more alarmist than usual.
• The three justices, all nominated by Democrats, argued the ruling could reshape the role of the executive branch in U.S. democracy.

Supreme Court Justices Sonia Sotomayor, Ketanji Brown Jackson and Elena Kagan laid out grim visions of U.S. democracy in their joint written dissents to the court's Monday decision on former President Donald Trump's claim of presidential immunity from criminal prosecution.

"In every use of official power, the President is now a king above the law," Sotomayor wrote. "This majority's project will have disastrous consequences for the Presidency and for our democracy."

Jackson echoed her warning: "If the structural consequences of today's paradigm shift mark a step in the wrong direction, then the practical consequences are a five-alarm fire that threatens to consume democratic self-governance and the normal operations of our Government."

As written opinions go, the dissenters' alarm was "definitely striking," said Alison LaCroix, a legal historian at the University of Chicago.

"It's a darker tone. It's more of a warning," LaCroix told CNBC in an interview about the three dissents, written by the only three justices nominated to the court by Democratic presidents.

In a 6-3 opinion along partisan lines, the Supreme Court on Monday ruled presidents are immune from criminal prosecution on a case-by-case basis, that they are exempt when charges relate to "official" presidential acts and not exempt from charges of "unofficial" acts.

The immediate effect was to send special counsel Jack Smith's criminal election fraud case against Trump back to U.S. District Judge Tanya Chutkan. She will have to rule on whether the criminal charges pertain to official acts Trump carried out as president, granting him immunity, or his private conduct.

The added complexity will almost certainly delay the trial until after the Nov. 5 election, a victory for Trump, the presumptive nominee, and the Republicans.

Chief Justice John Roberts attempted to present the majority opinion as a modest move, which is why the dissenters felt a need to deliver such notably fiery pushback, LaCroix said.

"Chief Justice Roberts, in the way that he often does, tried to occupy a kind of middle ground of moderation and the court as an institution," LaCroix said. "The dissents really point back at that and say, 'Listen, you need to acknowledge or own that this is as big of a deal as it is.'"

Sotomayor wrote, "The long-term consequences of today's decision are stark. The Court effectively creates a law-free zone around the President, upsetting the status quo that has existed since the Founding."

The dissenters, all of whom were appointed by Democratic presidents, argued the ruling will expand executive power beyond anything the justices can imagine today.

They also laid out several hypothetical scenarios of presidential crimes that they claimed would now be difficult or impossible to prosecute.

For example, if the president "orders the Navy's Seal Team 6 to assassinate a political rival? Immune," wrote Sotomayor. "Organizes a military coup to hold onto power? Immune. Takes a bribe in exchange for a pardon? Immune. Immune, immune, immune."

Whether a president is immune "from legal liability for murder, assault, theft, fraud, or any other reprehensible and outlawed criminal act" will now "always and inevitably be: It depends," wrote Jackson.

"Even if these nightmare scenarios never play out, and I pray they never do, the damage has been done," Sotomayor added.

LaCroix said that while these hypotheticals are extreme and "obviously rhetorical," they are not complete hyperbole.

"I think what we've seen in the last five or six years is that anything someone can come up with as a hypothetical, increasingly, is something that actually happens or might happen," she said.

"We've seen a lot of norms just get blown away. I feel like the lesson of the last half-decade or so has been, don't assume that anything is completely off the table."