The US White House has lambasted Democrats for launching a “disgraceful” inquiry into alleged obstruction of justice and abuse of power by some of President Donald Trump’s closest allies.
A White House spokeswoman said the Democrats were “harassing” Mr Trump.
Earlier on Monday, the House Judiciary Committee had requested documents from 81 people and groups.
Among them were aides to President Trump and his campaign, members of his family, business associates and others.
House of Representatives Judiciary Committee Chairman Jerry Nadler, a Democrat, said it was the “obligation” of Congress to “provide a check on abuses of power” by the White House.
Mr Nadler, whose committee has the power to conduct impeachment hearings, also said it was “very clear” that the president had obstructed justice.
But Mr Nadler told ABC News it was too early to discuss removing the president from office.
President Trump dismissed Mr Nadler’s probe as a “political hoax”, but added: “I co-operate all the time with everybody.”
Democrats, who took control of the House of Representatives in January, have vowed to open investigations into the president and White House