Dershowitz says quid pro quos directed at reelection cannot be impeachable

The flip side: Lead House impeachment manager Rep. Adam Schiff replied: "I would assume in every impeachment case, yes, you have to show the president was operating from a corrupt motive, and we have."

The big picture: Senators began the 16-hour question-and-answer phase of the impeachment trial on Wednesday. Both sides will have eight hours over the next two days to submit pre-written questions to Supreme Court Chief Justice John Roberts, who will direct them to House impeachment managers or Trump's legal team for five-minute responses.

• Whether to call witnesses remains a looming issue among lawmakers as senators gear up for a vote on Friday.

Go deeper... Live updates: Senators to get their turn for questions