Sen. Ron Wyden, the top-ranking Democrat on the Senate Finance Committee, is calling on the Treasury Department to disclose banking and real estate records associated with President Trump's sale of a Palm Beach, Fla., mansion to a Russian billionaire.

Trump sold the property in 2008 for $95 million to Russian oligarch Dmitry Rybolovlev, after purchasing it for $45 million four years earlier. Trump has attributed the flip to renovations he made on the property. At the time it was considered one of the most expensive house sales on record.

“It is imperative that Congress follow the money and conduct a thorough investigation into any potential money laundering or other illicit financial dealings between the president, his associates, and Russia,” Wyden, D-Ore., wrote in a letter to Steven Mnuchin, the treasury secretary.

In the letter, Wyden noted the deal occurred at a time that reports showed Trump had trouble finding banks to lend him money. The sale of the mansion happened a few months before before Trump Entertainment Resorts filed for Chapter 11 bankruptcy.

Wyden is part of the Senate Intelligence Committee, which is investigating Russian meddling in the 2016 election and whether the Trump campaign colluded with Russia to influence the outcome. Rybolovlev is being looked at by special counsel Robert Mueller, according to a Bloomberg report.

Trump has said that this mansion is one of the only deals he had ever made involving someone from Russia.

“The primary thing I did with Russia, I bought a house in Palm Beach at a bankruptcy … I bought it for about $40 million," he said in an ABC interview. "I sold it for $100 million to a Russian,” Trump said. “And that was primarily it.”