Congressional committees are also reviewing ethical and policy concerns that filter into numerous Cabinet agencies, including Trump's proposal to house migrants in so-called sanctuary cities.
Some of the Democrats' efforts could lay the groundwork for impeachment proceedings. They've asked for reams of documents from dozens of witnesses to assess whether the president obstructed justice, acted corruptly or otherwise abused his power.
Trump's latest comments were prompted by questions over whether he would fight a congressional subpoena issued to Don McGahn, his former White House counsel who served as a star witness for Mueller. According to Mueller's report, McGahn resisted Trump's pressure to fire the special counsel and subsequently to falsely deny he was asked to do so. At one point McGahn complained that the president wanted him to do "crazy s--t," the report said.
Trump called the subpoena "ridiculous," while repeating his assertion that the Mueller investigation was a witch hunt conducted by people who hate him "with a passion."
"Now we're finished with it, and I thought after two years we'd be finished with it," he said. "No. Now the House goes and starts subpoenas. They want to do every deal I've ever done."
Though Trump argued during the inquiry that any investigation into his finances would constitute a red line, he said Wednesday that he assumed Mueller had looked at all of his tax and financial documents. And though he was the first president in decades who has not released his tax returns, he misleadingly claimed that his financial documents have been widely seen by the public.
Trump and his company have also sued to block a subpoena for business records by saying it served no "legitimate legislative purpose."
Democrats call Trump's efforts to defy their oversight unprecedented and have been complaining for months about his lack of cooperation.
The U.S. Treasury missed a congressional deadline Tuesday to turn over Trump's tax returns to the House Ways and Means Committee, promising to respond further by May 6. Ways and Means and two other congressional committees have the authority to review individual tax returns under a law passed by Congress almost a century ago.
White House officials also directed Carl Kline, who oversaw the security clearance process, not to appear at a deposition, prompting the House Oversight Committee to consider contempt proceedings.