"So I think it's very sad for our country, I think it makes it harder to do my job," Trump said at the White House. "But I do my job and I do it better than anybody's done it for the first two and half years based on results."
In a pair of subpoenas, the House intelligence committee said the Department of Defense and the White Office of Management and Budget must turn over the documents by Oct. 15.
On Sunday, lawyers said a second whistleblower had come forward to substantiate an August complaint from an unnamed U.S. government official, which touched off the investigation.
Diplomatic text messages released by Democrats last week show that U.S. officials were involved in the effort to secure a public commitment from Ukraine to look into the business dealings of Hunter Biden.
Trump has alleged that Hunter Biden profited in his business dealings in both Ukraine and China from his father's position, and that Joe Biden, as vice president, pushed Ukraine to fire a prosecutor to impede a probe of a company tied to his son.
There has been no evidence of wrongdoing on the part of either Biden.
Trump's White House could formally tell House Speaker Nancy Pelosi as early as Monday that it will ignore lawmakers' demands for documents until the Democratic-controlled House of Representatives holds a vote to formally approve the impeachment inquiry.
Pelosi says a vote is not needed, but Democrats say she would prevail if one were held, although very few Republicans would be expected to side with the Democratic majority. Congress returns to Washington on Oct. 15 after a two-week recess.
The impeachment investigation could lead to the approval by the House of formal charges against Trump.
A trial on whether to remove him from office would then be held in the Republican-controlled Senate, but few Republicans have broken ranks with Trump so far for asking Ukraine and China to launch investigations of Biden, a former vice president and leading contender for the Democratic nomination to face Trump in the November 2020 presidential election.