AND THE WALLS COME TUMBLIN':

Donald Trump's impeachment blockade has collapsed.

The president's former top Russia adviser, Fiona Hill -- the first White House official to cooperate in Democrats' investigation of the Ukraine scandal -- has sketched for lawmakers a trail of alleged corruption that extends from Kiev to the West Wing. In dramatic testimony on Monday, she roped in some of Trump's top advisers as witnesses to the unfolding controversy.

And on Tuesday, a senior State Department official, George Kent, appeared on Capitol Hill to testify about his knowledge of the episode despite an attempt by administration lawyers to block him, according to a source working on the impeachment inquiry. The House Intelligence Committee issued a subpoena for his testimony Tuesday morning, and Kent complied.

It's the latest evidence that the White House's stonewalling against congressional requests for documents and testimony is crumbling -- and Democrats are feeling a new sense of momentum.

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