Republicans Shift Defense of Trump Who Launches New Attack on Key Witness

But as is perpetually the case with the President, a brew of competing scandals and controversies will jostle for attention in Washington. That includes fallout from a mysterious and unscheduled trip to a hospital on Saturday, his fight against efforts to reveal his tax records and an apparent new tactic -- firing off searing attacks on witnesses who criticize him in televised hearings.

The President opened a window into the state of his mind Sunday when he lashed out against Jennifer Williams, an aide to Vice President Mike Pence, who described his July 25 call with Ukrainian President Volodymyr Zelensky in her deposition as "inappropriate."

An appearance on Wednesday from Gordon Sondland, the US envoy to the European Union, could prove to be the most pivotal moment so far of the inquiry into whether Trump abused his power.

The former GOP donor is emerging as Trump's top point of contact with Ukranian officials as the President pushed for an investigation into former Vice President Joe Biden, a possible 2020 rival.

Other witnesses have testified that Sondland had a direct line to the President and as saying that the only thing Trump cared about in relations with Ukraine was his own political advantage, CNN reported.

That leaves Sondland facing a dilemma -- does he seek to protect the President when he testifies under oath or can he mitigate his own exposure? He may not be able to do both.

But Sondland is not the only witness with the capacity to damage the President's case this week. At least eight current and former officials are expected to testify in a dramatic week of televised hearings that are likely to infuriate Trump and may tie him more directly to the scheme to go around official US foreign policy channels to heap pressure on Ukraine.

Trump blasted Williams in a tweet as part of a band of "Never Trumpers, who I don't know & mostly never even heard of." Pence's office pointedly declined to defend Williams -- with a spokeswoman apparently seeking to downplay her importance to the Vice President by saying she was a staffer on assignment from the State Department.

The President's attack may be an attempt to discredit public testimony from Williams due on Tuesday when she is scheduled to appear alongside Lt. Col. Alexander Vindman, a senior National Security Council official who has also criticized Trump.

Trump's assault follows his attack on former US ambassador to the Ukraine Marie Yovanovitch during her testimony at a televised hearing on Friday in a tweet that sparked a debate over whether he was guilty of witness tampering -- with some Democrats suggesting the episode could be folded into articles of impeachment.