The last decision of the Supreme Court term may be its most impactful ... but perhaps not as impactful as some may think. On a 6-3 decision written by Chief Justice John Roberts, the court ruled that the constitutional separation of powers provides presidents with "absolute immunity" from prosecution for official acts in office -- in terms of 'core' constitutional duties. 

As for other official acts, the court rules that presidents should have the preumption of immunity, but that courts could consider that application on a case-by-case basis. However, Roberts warned with significant portent, presidents have no presumption of immunity from unofficial acts in office:

The parties before us do not dispute that a former President can be subject to criminal prosecution for unofficial acts committed while in office. See Tr. of Oral Arg. 28. They also agree that some of the conduct described in the indictment includes actions taken by Trump in his unofficial capacity. See id., at 28–30, 36–37, 124. 

They disagree, however, about whether a former President can be prosecuted for his official actions. Trump contends that just as a President is absolutely immune from civil damages liability for acts within the outer perimeter of his official responsibilities, Fitzgerald, 457 U. S., at 756, he must be absolutely immune from criminal prosecution for such acts. Brief for Petitioner 10. And Trump argues that the bulk of the indictment’s allegations involve conduct in his official capacity as President. See Tr. of Oral Arg. 30–32. Although the Government agrees that some official actions are included in the indictment’s allegations, see id., at 125, it maintains that a former President does not enjoy immunity from criminal prosecution for any actions, regardless of how they are characterized. See Brief for United States 9. 

We conclude that under our constitutional structure of separated powers, the nature of Presidential power requires that a former President have some immunity from criminal prosecution for official acts during his tenure in office. At least with respect to the President’s exercise of his core constitutional powers, this immunity must be absolute. As for his remaining official actions, he is also entitled to immunity. At the current stage of proceedings in this case, however, we need not and do not decide whether that immunity must be absolute, or instead whether a presumptive immunity is sufficient. 

It's reasonable to note that the issues in the prosecutions of Donald Trump do not involve 'core' constitutional duties. To the extent that they involve official acts -- such as in the January 6 riot -- the courts will still have to suss out whether those are covered by presumptive immunity, as well as which acts are official and which are private.

Roberts notes that the courts involved in these prosecutions have yet to address those questions, necessarily because of the unknown validity of the immunity claims:

Despite the unprecedented nature of this case, and the very significant constitutional questions that it raises, the lower courts rendered their decisions on a highly expedited basis. Because those courts categorically rejected any form of Presidential immunity, they did not analyze the conduct alleged in the indictment to decide which of it should be categorized as official and which unofficial. Neither party has briefed that issue before us (though they discussed it at oral argument in response to questions). And like the underlying immunity question, that categorization raises multiple unprecedented and momentous questions about the powers of the President and the limits of his authority under the Constitution. As we have noted, there is little pertinent precedent on those subjects to guide our review of this case—a case that we too are deciding on an expedited basis, less than five months after we granted the Government’s request to construe Trump’s emergency application for a stay as a petition for certiorari, grant that petition, and answer the consequential immunity question. See 601 U. S., at ___. Given all these circumstances, it is particularly incumbent upon us to be mindful of our frequent admonition that “[o]urs is a court of final review and not first view.” Zivotofsky v. Clinton, 566 U. S. 189, 201 (2012) (internal quotation marks omitted).

Roberts attempts to set up some guidelines for lower courts, again a necessity springing from the novelty of this ruling. Special counsel Jack Smith can't be too happy with the parameters drawn by the majority:

But the breadth of the President’s “discretionary responsibilities” under the Constitution and laws of the United States “in a broad variety of areas, many of them highly sensitive,” frequently makes it “difficult to determine which of [his] innumerable ‘functions’ encompassed a particular action.” Id., at 756. And some Presidential conduct—for example, speaking to and on behalf of the American people, see Trump v. Hawaii, 585 U. S. 667, 701 (2018)—certainly can qualify as official even when not obviously connected to a particular constitutional or statutory provision. For those reasons, the immunity we have recognized extends to the “outer perimeter” of the President’s official responsibilities, covering actions so long as they are “not manifestly or palpably beyond [his] authority.” Blassingame v. Trump, 87 F. 4th 1, 13 (CADC 2023) (internal quotation marks omitted); see Fitzgerald, 457 U. S., at 755–756 (noting that we have “refused to draw functional lines finer than history and reason would support”). 

In dividing official from unofficial conduct, courts may not inquire into the President’s motives. Such an inquiry would risk exposing even the most obvious instances of official conduct to judicial examination on the mere allegation of improper purpose, thereby intruding on the Article II interests that immunity seeks to protect. ... 

Nor may courts deem an action unofficial merely because it allegedly violates a generally applicable law. 

Roberts has already cut off a couple of arguments from Smith. The indictment alleged that Trump used the Department of Justice to perform a "sham" election-fraud probe in an effort to overturn the election. However, the DoJ falls entirely within the president's constitutional authority, and so ...

The indictment’s allegations that the requested investigations were “sham[s]” or proposed for an improper purpose do not divest the President of exclusive authority over the investigative and prosecutorial functions of the Justice Department and its officials. App. 186–187, Indictment ¶10(c). And the President cannot be prosecuted for conduct within his exclusive constitutional authority. Trump is therefore absolutely immune from prosecution for the alleged conduct involving his discussions with Justice Department officials. 

Similarly, Roberts writes that the allegations of attempting to corrupt the process used by Mike Pence in his role as President of the Senate could involve presidential immunity. Roberts doesn't flat-out negate that part of the indictment, given that Pence operated in that function as part of the legislative branch, but directed the lower courts to carefully conside the VP's normal role as a member of the executive branch.

However, Roberts makes a point of noting where presumptive immunity ends in this particular case:

Unlike the allegations describing Trump’s communications with the Justice Department and the Vice President, these remaining allegations involve Trump’s interactions with persons outside the Executive Branch: state officials, private parties, and the general public. Many of the remaining allegations, for instance, cover at great length events arising out of communications that Trump and his co-conspirators initiated with state legislators and election officials in Arizona, Georgia, Michigan, Pennsylvania, and Wisconsin regarding those States’ certification of electors. See App. 192–207, Indictment ¶¶13– 52. ...

Unlike Trump’s alleged interactions with the Justice Department, this alleged conduct cannot be neatly categorized as falling within a particular Presidential function. The necessary analysis is instead fact specific, requiring assessment of numerous alleged interactions with a wide variety of state officials and private persons. And the parties’ brief comments at oral argument indicate that they starkly disagree on the characterization of these allegations. The concerns we noted at the outset—the expedition of this case, the lack of factual analysis by the lower courts, and the absence of pertinent briefing by the parties—thus become more prominent. We accordingly remand to the District Court to determine in the first instance—with the benefit of briefing we lack—whether Trump’s conduct in this area qualifies as official or unofficial.

[more to come]