Donald Trump has not been subtle about his desire to undermine or undercut special prosecutor Robert Mueller’s Russian collusion investigation—particularly in regards to pardons. Shortly after news broke that the former F.B.I. chief was sniffing around his family’s finances and the Trump Organization’s business deals, Trump boasted on Twitter that he has the “complete power to pardon.”

But Trump may have prematurely shown his hand. Mueller’s A-team of top investigators and attorneys has reportedly begun researching just how “complete” Trump’s pardon power really is, and whether he could pre-emptively pardon his family members and close associates. Specifically, the special prosecutor’s top legal counsel, Michael Dreeben, is looking into past presidential pardons to determine what restrictions exist, according to a Bloomberg report published Tuesday.

Dreeben is venturing into uncharted territory. As Mueller’s investigation was metastasizing at the end of July, The Washington Post reported that Trump had begun asking his advisers and legal team about his ability to pardon aides, associates, family members, and even himself—questions Dreeben is likely seeking the answers to himself. “While there has been a lot of speculation over the past months, the language about the pardon power in the Constitution is very broad and the unusual circumstances commentators (and now Dreeben) are considering [have] never happened before,”Renato Mariotti, a former federal prosecutor, wrote on Twitter. “Mueller and Dreeben are likely planning their legal argument in advance as well as plotting out next steps in case the President issues pardons that could otherwise hinder the investigation.”

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Dreeben’s research project is not the first indication that Mueller is preparing for Trump to exercise his pardon power, either. In August, Politico reported that Mueller and New York Attorney General Eric Schneiderman had joined forces and begun sharing evidence from their parallel probes into Paul Manafort, Trump’s former campaign chairman. Manafort has emerged as a key figure in Mueller’s investigation. At the end of July, F.B.I. investigators raided Manafort’s Virginia home, reportedly seeking documents, at which time Mueller reportedly told the longtime political consultant and lobbyist that he would soon be indicted. (Manafort has repeatedly denied any wrongdoing.)

Some have speculated that Trump could pardon Manafort—along with former national security adviser Mike Flynn, another subject of the F.B.I. investigation—for any crimes uncovered in the Justice Department probe. But in partnering with Schneiderman, Mueller potentially took this option off the table, as the president’s power to pardon only applies to federal crimes. In other words, if Schneiderman’s office brought charges against Manafort at the state level, a pardon from Trump would be useless.