Trump trial nightmare? WH aides have legal duty to testify

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Donald Trump’s impeachment is teeing up a clash over whether the Senate will call witnesses to testify about his Ukraine plot, and in this special report, MSNBC Chief Legal Correspondent Ari Melber breaks down how cabinet officials have a Constitutional obligation to testify. The segment reports on basic fact often overlooked in recent impeachment debates, many of the witnesses key to the case have already testified before Congress several times over matters far less important than the Ukraine scandal that got Trump impeached, including current government officials like Sec. Pompeo and Atty. Gen Barr.