Does a District Attorney (DA) have the power to launch a criminal inquiry into the unofficial actions of the President? For the investigative methods at issue in Trump v. Vance the Second Circuit said "yes." The decision focused on whether a New York state grand jury subpoena could obtain the President's tax returns from Mazars LLC, an independent accounting and tax service. But stepping away from the case's facts, the Circuit's ruling potentially stands for the proposition that a state grand jury subpoena can force a third party to turn over the president's personal records.

On Friday, the Supreme Court granted Trump's request to hear the case, but the Second Circuit's approach still merits some consideration. There are potential downsides to giving any DA with jurisdiction and probable cause the power to indirectly investigate the president for malfeasance. But if a DA is acting in good faith, there are a number of compelling reasons why s/he should be able to indirectly investigate a president's legally dubious actions.

In this case, Manhattan District Attorney Cyrus Vance served a grand jury subpoena on Mazars to obtain all of the firm's records related to Trump's personal tax filings and business dealings. DA Vance was looking for records of alleged "hush money" payments to two women that were written off as business expenses during the presidential campaign. In response to the subpoena, Trump filed an action in federal court asserting he had broad presidential immunity from any state criminal investigation.

The Second Circuit narrowly construed the case and found "that presidential immunity does not bar the enforcement of a state grand jury subpoena directing a third party to produce non-privileged material, even when the subject matter under investigation pertains to the president." To support this ruling the Second Circuit turned to United States v. Burr where the Supreme Court held that "the president of the United States may be subpoenaed, and examined as a witness, and required to produce any paper in his position," and the Supreme Court's observation in United States v. Nixon that the exercise of jurisdiction over the president is warranted when necessary "to vindicate the public interest in an ongoing criminal proceeding." The Second Circuit acknowledged that these cases did not deal with state investigations and "any direct control by a state court over the President may implicate concerns under the Supremacy Clause." But the circuit panel unanimously concluded the subpoena at issue was not exercising direct control over the President because it was written to obtain Mazars's records. This holding appears to allow DAs to open investigations into a president's unofficial activities and, so long as the investigation seeks records from a third party, requires adherence to a state grand jury subpoena. This result has significant implications for future investigations into presidential malfeasance by state, as opposed to federal, officials.

The Trump administration has had an uncharacteristically large number of scandals related to potential corruption, conflicts, and self-dealing. According to the New York Times, the President still profits from these interests via a trust managed by his two eldest sons and a Trump Organization executive. Consequently, president Trump's potential self-dealing needs to be carefully monitored (see Trump's attempt to host the G-7 summit at one of his hotels). The Second Circuit's decision to uphold the grand jury subpoena has the potential to become a powerful check on presidential corruption or malfeasance in the future. Specifically, giving DAs jurisdiction and subpoena power over the president's private activity could have three positive effects:

(1) It provides the American people with another set of eyes capable of ensuring the president does not commit any criminal acts in his personal capacity.

(2) Aside from a court order, a DA's case or legal process is immune from federal interference. This means that the president does not have any official power to alter a DA's investigation or conclusions.

(3) A president inclined to take an illegal action might think twice if s/he knows that a county or city DA, or state AG, could launch a separate investigation over which s/he would have almost no control.

But, giving every DA this power also has potential drawbacks. In this case, the Manhattan District Attorney has clearly established probable cause for pursuing this case and appears to be meticulously collecting the requisite evidence. But less careful state prosecutors might have an incentive to use this investigative power to obtain public notoriety by launching high-profile investigations into a president they oppose or out of a desire to damage an opposing party's administration.

However, DAs who might be inclined to overzealously investigate a president are still restricted by state and federal constitutions, the courts, and public opinion. In the first instance, no prosecutor can pursue an investigation without some reliable information giving him/her probable cause to start the case. Furthermore, even if a DA had probable cause, the potentially criminal activity would need to have occurred in the prosecutor's jurisdiction. After these two bars are passed, under the Second Circuit's logic, the president's lawyers could still get a federal court to enjoin a DA's subpoenas by showing that adhering to the subpoena could cause irreparable harm and either the president is likely to succeed on the merits of the case or the subpoena presents a balance of hardships tipping decidedly in favor of the president.

Finally, beyond a subpoena's legal requirements, even if initiating an investigation is popular among a DA's electorate, failing to successfully find a criminal offense would likely sour public opinion against a DA. This could very quickly turn what would initially appear to be a political windfall into a liability. Collectively, these factors suggest that a DA is unlikely to abuse a grand jury's subpoena power. Thus, the benefits of such a system appear to outweigh its costs.

The private actions of a president are subject to the investigative powers of a DA or state prosecutor in a very rare set of cases. But as the federal government fails to seriously investigate the President's alleged, but corroborated, corruption, self-dealing and malfeasance, some DAs have filled this void. If the Supreme Court upholds the Second Circuit's approach in Trump v. Vance it could cement federalism's increasingly important role in national public integrity cases—giving the American people an unexpected, yet critical, safety valve to tackle executive corruption.

Jacques Singer-Emery is a student at Harvard Law School and previously spent four years in the New York Police Department (NYPD), first as a policy advisor to Police Commissioner Bratton and then as a case analyst for the NYPD Intelligence Bureau. He is the editor-in-chief of the National Security Law Journal.