The Senate committee also has received reports from the Treasury Department’s Financial Crimes Enforcement Network, which tracks illicit money flows, to learn if any of Mr. Trump’s businesses may have financial ties to Russian interests, these people said. Mr. Trump has said he has no such ties.

Mr. Manafort, a Republican political consultant, spent years working for a pro-Russia party in Ukraine. He served as Mr. Trump’s presidential campaign manager for roughly three months in 2016 before resigning.

New York Attorney General Eric Schneiderman and Manhattan District Attorney Cyrus Vance Jr. also are investigating Mr. Manafort’s real-estate transactions, The Wall Street Journal has reported, with both offices examining his dealings for possible money-laundering and fraud. Messrs. Schneiderman and Vance are Democrats.