The indictment of President Trump on 34 counts handed up by the district attorney of New York County, Alvin Bragg, brings into focus the decisions by both his predecessor, Cyrus Vance Jr., and  federal prosecutors not to pursue charges against the former president. 

If they passed, the thinking goes, why didn’t New York’s top prosecutor do so as well? Also, because they did, might he be prevented from securing a conviction? The exercise of their discretion casts a shadow on Mr. Bragg’s decision.

It could also, owing to an idea at the core of the Framers’ design, present a boon to Mr. Trump’s lawyers in their effort to scotch Mr. Bragg’s case before it even reaches a jury. For the doctrine of preemption ordains that when two bodies of law come into conflict, the higher authority displaces the lower one.

In America, federal law preempts state law, and state law generally preempts local law, though there are exceptions carved out to account for particular interests of localities. Generally, though, federal law owes its preeminence to the “Supremacy Clause.”

That celebrated clause states: “This Constitution, and the laws of the United States which shall be made in pursuance thereof; and all treaties made, or which shall be made, under the authority of the United States, shall be the supreme law of the land; and the judges in every state shall be bound thereby, anything in the Constitution or laws of any State to the contrary notwithstanding.”

In the absence of federal law, state law holds. The integrity of state power is found the Constitution’s 10th Amendment, which dictates that the “powers not delegated to the United States by the Constitution, nor prohibited by it to the states, are reserved to the states respectively, or to the people.” State authority, in other words, governs where federal power is unenumerated.

That clause is Mr. Bragg’s lifeline.The 34 counts of Mr. Trump’s indictment — each a check or ledger entry — become felonious only when combined with another crime. On their own, falsifying business records is merely a misdemeanor in New York. In other words, Mr. Bragg needs an underlying crime to transform the laundry list of charges into a battery of felonies. 

The nature of that underlying crime is shrouded in mystery. It is absent from the four corners of the indictment. At Mr. Bragg’s press conference after Mr. Trump’s arraignment, the district attorney allowed that the “indictment doesn’t specify” an underlying crime “because the law does not so require.”

Mr. Bragg did go on to mention “New York State election law, which makes it a crime to conspire to promote a candidacy by unlawful means,” but Mr. Trump was a candidate for federal office, and — cue the doctrine of preemption — it is unsettled to what extent he was bound by state law. 

This is where the decision by prosecutors not to charge Mr. Trump — even as they secured a plea bargain for his former attorney, Michael Cohen, that stemmed from the same facts — could prove salient. Mr. Trump could attempt a move to federal court, arguing that he was running for president or serving in that office when the crimes were allegedly committed.

Expect his attorneys to claim that Mr. Bragg overstepped. With the Department of Justice showing no inclination to prosecute, at least on this score, Mr. Trump could walk out of federal court a free man, if he is forced to walk in it at all. 

The former president could have one final avenue to avoid the specter of prison. Should Mr. Trump be convicted on federal charges, one of his rivals for the 2024 Republican nomination, Vivek Ramaswamy, has already promised him a pardon, should the entrepreneur win the White House.