Manhattan D.A. Intensifies Investigation of Trump

State prosecutors in Manhattan have interviewed several employees of President Trump’s bank and insurance broker in recent weeks, according to people with knowledge of the matter, significantly escalating an investigation into the president that he is powerless to stop.

The interviews with people who work for the lender, Deutsche Bank, and the insurance brokerage, Aon, are the latest indication that once Mr. Trump leaves office, he still faces the potential threat of criminal charges that would be beyond the reach of federal pardons.

It remains unclear whether the office of the Manhattan district attorney, Cyrus R. Vance Jr., will ultimately bring charges. The prosecutors have been fighting in court for more than a year to obtain Mr. Trump’s personal and corporate tax returns, which they have called central to their investigation. The issue now rests with the Supreme Court.

But lately, Mr. Vance’s office has stepped up its efforts, issuing new subpoenas and questioning witnesses, including some before a grand jury, according to the people with knowledge of the matter, who requested anonymity because of the sensitive nature of the investigation.

The grand jury appears to be serving an investigative function, allowing prosecutors to authenticate documents and pursue other leads, rather than considering any charges.

When Mr. Trump returns to private life in January, he will lose the protection from criminal prosecution that his office has afforded him. While The New York Times has reported that he discussed granting pre-emptive pardons to his eldest children before leaving office — and has claimed that he has the power to pardon himself — that authority applies only to federal crimes, and not to state or local investigations like the one being conducted by Mr. Vance’s office.