The implication of the Vice President, the Secretary of State, and the Attorney General in the Ukraine extortion and coverup gives impeachment investigators key leverage. It is investigative SOP to exploit any daylight between the principal and the facilitators and Adam Schiff is a former federal prosecutor. If the facilitators see their own jeopardy as separable from Trump's, they may affect that separation: by serving as catalyst to get to critical mass in the Cabinet to trigger the 25th Amendment or, as John Dean did to Nixon, by agreeing to cooperate and testify in the House impeachment, which is now all but certain.