Merkley argued the handling of Kavanaugh's nomination is "an assault on the separation of powers" and violates the Constitution. Merkley said his lawsuit will be filed later Wednesday in federal court in Washington, D.C., and would ask the court to block a vote until documents are handed over.

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Merkley, speaking to reporters on Wednesday , laid out three acts where he thought the White House had directly interfered with the Senate's "advice and consent" responsibly: blocking access to staff secretary documents, blocking access to some documents from Kavanaugh's work as a White House lawyer and labeling some documents given to the Senate Judiciary Committee "committee confidential."

Merkley acknowledged that he did not know of a precedent where a court prevented a Senate vote, but he said he was also not aware of a time where he claims the White House had so "profoundly interfered" on a Supreme Court nominee's documents.

"This is unchartered territory," he said.

Merkley's lawsuit comes as Kavanaugh and Christine Blasey Ford, the first woman to publicly accuse him of sexual assault, are scheduled to testify before the Judiciary Committee on Thursday .

Kavanaugh has denied wrongdoing and pledged that he will not withdraw his nomination, even as two other women have come forward to accuse him of misconduct stemming from his time in high school and college in the 1980s.