Trump's tax documents are with New York prosecutors. But the clock is ticking.

Second, financial investigations are time consuming, and a U.S. president under criminal investigation has a number of tools at his disposal that can burn up even more time before the statute of limitations kicks in.

Trump’s challenges to the Mazars USA subpoena, most of which pertained to his unique position as president of the United States, are a good example: the Manhattan District Attorney’s Office, under Vance, opened its criminal investigation in the summer of 2018. Its subpoena to Mazars USA was issued Aug. 29, 2019. Trump’s first court challenge to the subpoena took place in the federal district court, then the federal appeals court, and eventually the U.S. Supreme Court, resulting in the Supreme Court’s first ruling against him July 9, 2020. Trump’s second court challenge followed the same laborious path to the Supreme Court, ending again in defeat on Feb. 22. The state prosecutors finally prevailed, but they were forced to spend one and a half years just trying to get the documents that are usually the starting point in a financial crimes investigation.