There is no indication that Cohen is a subject or target of the investigation into Russian interference in the 2016 election. But the scrutiny of his interactions is another sign of the far-reaching nature of the special-counsel probe, which is examining members of the president’s inner circle and aspects of Trump’s past business outreach to Russia.

As one of Trump’s closest advisers, Cohen played a role in at least two episodes involving Russian interests that have drawn Mueller’s attention, according to several people familiar with document subpoenas and witness interviews.

One area of focus has been negotiations Cohen undertook during the campaign to help the Trump Organization build a tower in Moscow. Cohen brought Trump a letter of intent in October 2015 from a Russian developer to build a Moscow project. Later, he sent an email to Russian President Vladi­mir Putin’s chief spokesman seeking help to advance the stalled project. He said he did not recall receiving a response.