WASHINGTON — The Democrats serving on the House Oversight Committee launched an investigation Tuesday into federal tax dollars being spent at President Donald Trump’s businesses.

The 18 lawmakers, led by Rep. Elijah Cummings of Maryland, sent letters to Cabinet secretaries and agency leaders requesting documents and asking how much their departments are spending on products or services provided by businesses owned by or affiliated with the Trump Organization. The responses are due Aug. 25.

“The President’s financial entanglements make it impossible to know whether he is making his decisions in the public interest or to benefit to him or his family members financially,” they write in the letters. “The President’s continued ownership of private businesses also places federal employees in compromised positions when they work on official activities that create financial benefits for the President or his family members.”

The lawmakers cite a litany of possible examples reported by various news organizations since the businessman became president nearly seven months ago:

The Department of Defense is renting space at Trump Tower, the Manhattan skyscraper that housed Trump’s business offices, his reality TV show and his presidential campaign.

Trump earns federal housing assistance money because of his partial ownership of Starrett City Associates, L.P., what has been called the nation’s largest federally subsidized residential property.

The State Department paid $9,510 for rooms to house the Secret Service when Trump’s son, Eric, visited Uruguay in January to promote a hotel and condo.

The State Department spent more than $15,000 on 19 rooms at a hotel in Vancouver, Canada, when Trump’s family headlined a grand opening celebration in February.

Trump has visited Mar-a-Lago on 25 days and his golf clubs on 48 days, sometimes more than once a day, according to a compilation of information released by the White House. He embarked on a 17-day vacation at the Trump National Golf Club in Bedminster, N.J., on Friday. Each trip costs taxpayers money, possibly millions of dollars.

“There may be other expenditures of American taxpayer funds at Trump properties that are not yet publicly known,” the lawmakers write in their letters. “Federal agencies and their employees may be hosting events or renting hotel rooms at Trump properties, eating meals at Trump property restaurants, or contracting for equipment rentals with Trump businesses.”

No Republicans, who control the committee chaired by Rep. Trey Gowdy of South Carolina, joined in the inquiry. Democrats working alone can launch their own investigation, but they do not have the power to subpoena documents.

The Trump administration had previously refused to respond to requests from the minority party, committee staffers say, but after criticism from Senate Judiciary Chairman Chuck Grassley, R-Iowa, and top Democrats, the White House appeared to reverse course.

Trump ignored calls to fully separate from his business interests when he became president. Instead, he placed his holdings in a trust.

An attorney who specializes in financial matters, including taxes, for affluent families who previously examined Trump’s available trust documents at the request of McClatchy noted that Trump amended an existing trust this year to name as trustees his son, Donald Jr., and Allen Weisselberg, the Trump Organization’s chief financial officer.

Trump retains the legal power to revoke the trust, the attorney said. The trust, which was to include all of Trump’s businesses, is designed to hold assets for his “exclusive benefit,” which he can receive at any time without the public’s knowledge, the attorney said.

Former White House Press Secretary Sean Spicer acknowledged in April that Trump could receive the money while president.

“The whole entire point of setting it up is so that somebody can draw money,” Spicer said. “The idea that the president is withdrawing money at some point is exactly the purpose of why a trust is set up, regardless of an individual.”