President Trump is reportedly apoplectic over the possibility that Special Counsel Robert Mueller might look into his finances—specifically his tax returns—as part of Mueller’s inquiry into Russian interference in the 2016 election. Trump suggested in a New York Times interview that would constitute a possible “violation,” and according to the The Washington Post the president is already looking into whether he can pardon associates, family members, and himself.

But there are no legal or ethical reasons for Mueller to turn away if, during his investigation, he discovers crimes that are unrelated to the original inquiry.

“Mueller is the Department of Justice for the purposes of this investigation," said John Q. Barrett, a former assistant counsel in the special prosecutor’s office during the Iran-Contra affair who is now a law professor at St. John’s University.

Mueller was appointed by Deputy Attorney General Rod Rosenstein after Trump fired then-FBI Director James Comey. Trump later acknowledged publicly that Comey was fired because of the federal investigation into whether there was collusion between the Trump campaign and what U.S. intelligence agencies have said was a Russian effort to help Trump win the 2016 election. Rosenstein, who had recommended Comey’s dismissal based on Comey’s public handling of the investigation into Hillary Clinton’s private email server, made the call to appoint Mueller because Attorney General Jeff Sessions had recused himself from the Russia investigation after reports revealed he had misled the Senate about the extent of his contacts with Russian officials during the 2016 campaign.