Read the full letter: White House says it won't cooperate in Trump impeachment inquiry

The escalation comes hours after the Trump administration blocked a key witness in the probe from testifying to Congress.

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By NBC News

The White House on Tuesday said it would not cooperate with House Democrats' impeachment inquiry, escalating the clash between Congress and President Donald Trump's administration.

In a letter that echoed Trump's recent messaging — accusing Democrats of violating the Constitution and civil liberties and attempting to overturn the results of the 2016 election — the White House called the impeachment inquiry invalid.

Read the full letter below, and read more about the latest developments in the impeachment investigation here.