The Supreme Court won't actually rule that the President is immune from prosecution. Think what Joe Biden could then do!
But they're all lawyers, so they understand that Trump's defense is completely factually and legally bankrupt. We've all seen and heard the proof, and it's unassailable. He attempted insurrection and the nullification of a legitimate election to retain power, he kept and refused to return national security documents and Presidential records that were in no sense personal documents, he exposed at least some of them to uncleared civilians and foreigners, he falsified business records (as he surely has his entire career), and he sexually assaulted Jean Carroll (not to mention many others, most likely).
The Republican Supremes know that Trump's defense is to run out the clock. Rich people use this defense to wear down prosecution all the time, and that's a fundamental problem for our legal system. It's why, for example, hardly any big corporation admits guilt in a settlement, and why the SEC among many other regulatory agencies almost always settles out of court instead of going to trial. It's also why no one significant ever did time for the manifest criminal financial behavior that led to the Great Recession in the aftermath of the subprime (and other) mortgage crisis.
Aileen Cannon, for all her reputation as being out of her depth in the documents case, cottoned onto Trump's interest and jumped enthusiastically into the tank long before the Republican Supremes. Delay? She's all over that!
What's my evidence?
If resolving a case helps Trump, the Supremes get right on it. They were never going to allow Colorado and other states to exclude Trump from the ballot, and they made that ruling tout suite. So, despite its plain history in the aftermath of the Civil War, they declared Section 3 of the Fourteenth Amendment not to be self-enforcing. Done and dusted.
On Presidential immunity though, they declined Jack Smith's filing for immediate certiorari. Hey, that gave them time to think up a path through the law that helps Trump. And, guess what, it's more delay!
Of course, Trump's interlocutory appeal for immunity will go nowhere in the law. It's a ridiculous, frivolous claim. The Supremes could have said so in their order declining cert, but that wouldn't help Trump delay and deny justice. Also, Trump's lawyers cannily filed an immunity motion in Cannon's courtroom, which means that eventually there will likely be competing rulings in different Federal Circuits, and only the Supreme Court can resolve those.
And, of course, it's not evidence about the Supreme Court, but it's evidence of the tactics of the Trump legal team: the Fani Willis/Nathan Wade affair. It has no real bearing on the case, but, Fani WTF?! It's a Bill Clinton level inability to stay focused. Eyes on the prize! Someone needs to get to trial before the fall, and you were our best hope. Instead, you couldn't keep your hands off someone who worked for you!
What we need: faster appeals courts, a limit to the number of issues a defendant can raise as interlocutories, and many fewer privileges for the powerful. I'm not holding my breath.