U.S. President Donald Trump is doubling down on his legal confrontations with Democrats in the House of Representatives.

Hours after his Treasury secretary again put off a House committee's demand for the president's tax returns, and as another panel was considering a contempt charge for a former White House aide for refusing to testify, Trump said in an interview that he was against having past and present administration officials taking part in various congressional inquiries.

He told The Washington Post that any further testimony is not necessary after the White House cooperated with special counsel Robert Mueller's investigation.