WASHINGTON — President Trump’s re-election campaign more than doubled its spending on legal fees over the past few months as its lawyers assisted the campaign in its handling of investigations into interactions between the president’s associates and Russia.

The committees devoted to Mr. Trump’s 2020 campaign spent nearly $700,000 on legal fees between the beginning of April and the end of June — more than twice as much as they spent in the first three months of the year — according to reports filed Saturday afternoon with the Federal Election Commission.

Among the legal fees paid by the Trump campaign was a $50,000 payment on June 27 to the offices of the New York lawyer Alan S. Futerfas, who is representing Donald Trump Jr. in the ongoing Russia-related investigations. Donald Jr. was recently thrust into the center of those investigations when The New York Times reported that he had arranged a meeting last year with a Russian lawyer who claimed to have damaging information about Hillary Clinton, who was set to become the Democratic presidential nominee.

Mr. Futerfas’s firm had not previously been paid by Mr. Trump’s campaign. Neither he nor Donald Jr. responded on Saturday to questions about the payment.

The majority of the legal payments reflected in the second-quarter reports — $545,000 — went to the law firm Jones Day. It has represented the campaign in election law matters and ongoing lawsuits, and is also advising it on legal issues related to the Russia investigations.

The campaign has been sending letters to former employees instructing them to retain documents that could be relevant to the ongoing investigations, according to several people who received them. Some of the letters, signed by the campaign’s executive director, Michael Glassner, alert the former employees that lawyers from Jones Day might contact them.

Representatives from Jones Day, the Trump campaign and the White House did not respond to questions about the firm’s role in helping the campaign navigate the Russia investigations, which have expanded to include several former campaign officials, as well as the campaign’s digital operation.

Federal election law permits campaign committees to pay legal fees incurred as a result of activity related to the campaign.

The Trump campaign also paid nearly $90,000 to the Trump corporation for legal consulting and $120,000 in rent for the campaign’s offices at Trump Tower in Manhattan.

In addition to the re-election campaign, two joint fund-raising vehicles established with Republican Party committees also filed…