President Donald Trump’s attorneys in the probe of Russian election interference are being funded in part through a Republican Party account with a handful of wealthy donors—including a billionaire investor, a property developer seeking U.S. government visas and a Ukrainian-born American who has made billions of dollars doing business with Russian oligarchs.

The Republican National Committee, through an account typically used for its own legal bills, paid more than $300,000 last month to help cover Mr. Trump’s private legal fees, according to filings with the Federal Election Commission.

The fund has also paid another nearly $200,000 to lawyers for the president’s eldest son, Donald Trump Jr., according to a person familiar with the payments. Those expenditures will be disclosed in the RNC’s September report, the person said.

The RNC legal fund in August raised about $280,000, according to FEC filings. The previous month, that fund raised more than $700,000. Mr. Trump’s re-election campaign has also contributed to the president’s personal legal expenses.

In past administrations, private legal fees have taken a significant toll on the first family’s personal finances. When former President Bill Clinton and Hillary Clinton left the White House in 2001, Mrs. Clinton’s financial disclosure showed they owed lawyers between $2.3 million and $10.6 million after years of scrutiny by Congress and independent counsel Ken Starr.