The White House has officially refused to co-operate with the impeachment inquiry against President Donald Trump.
A letter sent to Democratic leaders rejected it as “baseless” and “constitutionally invalid”.
Three Democratic-led House committees are investigating Mr Trump.
The White House letter comes hours after the Trump administration blocked the US ambassador to the European Union from appearing before a congressional impeachment investigation.
What does the letter say?
White House counsel Pat Cipollone addressed the eight-page letter to the leading Democrat and House Speaker, Nancy Pelosi, and the three chairmen of the Democratic committees.
He accused the leaders of setting up an inquiry “that violates fundamental fairness and constitutionally mandated due process” – specifically by not holding a vote on launching the inquiry.
“Mr President, you are not above the law. You will be held accountable.”
Two weeks into the House of Representative’s impeachment inquiry, the US is approaching a constitutional crisis.
While the White House’s written response to Speaker Nancy Pelosi took eight pages, the message was simple. No depositions. No documents. No co-operation whatsoever.
Democrats at this point have several options. They could cite the administration for obstruction and make that, itself, an article of impeachment.
They could attempt to accommodate the White House’s unspecified demands, hoping to encourage its assistance.
Or they could try to use the courts to compel the White House to co-operate.
This is uncharted territory. And as both sides acknowledge (albeit drawing entirely different conclusions), the presidency – and perhaps the rule of law itself – are at stake.
What’s the latest in the impeachment inquiry?
Mr Cipollone’s letter comes hours after the White House blocked Gordon Sondland, the US ambassador to the EU, from speaking to the three Democratic committees behind closed doors.
Text messages released last week show Mr Sondland discussed efforts to pressure Ukraine over Mr Biden with other US diplomats.
“Ambassador Sondland believes strongly that he acted at all times in the best interests of the United States, and he stands ready to answer the Committee’s questions fully and truthfully,” the statement said.
In a tweet, the president said Mr Sondland would only have been appearing before a “kangaroo court”.
Why is there an impeachment inquiry?
The Democratic-led inquiry is seeking to find out if the president withheld nearly $400m (£327m) in aid to pressure Ukraine’s President Volodymyr Zelensky to set up an inquiry into Mr Biden.
Hunter, Mr Biden’s son, once sat on the board of a Ukrainian energy company.
Mr Trump and his supporters believe Joe Biden used his position as vice president to force Ukraine to drop a probe into the company that could have implicated his son in wrongdoing.
What is impeachment?
Impeachment is the first part – the charges – of a two-stage political process by which Congress can remove a president from office.
If the House of Representatives votes to pass articles of impeachment, the Senate is forced to hold a trial.