Now, another perspective on the Senate Impeachment trial of President Trump, which continues today at 1:00. As always, we will bring you NPR’s live coverage at that time. Both the House impeachment managers and the White House defense team have now wrapped up their arguments. Today, the trial moves into the "Question" phase. During the next 16 hours, senators will submit questions to Chief Justice John Roberts, who will read them aloud and ask House managers and White House lawyers to respond. Sure to be among the topics is the possibility of calling witnesses like former National Security Advisor John Bolton. On Sunday night, when the New York Times published a story about a book Mr. Bolton has written describing Bolton’s interactions with the President on the subject of withholding aid to Ukraine, the dynamics of the trial changed dramatically. To help us understand the moving parts in this historic process, we're joined by one of the nation's foremost constitutional scholars. Kim Wehle is a professor of law at the University of Baltimore, and currently a visiting professor and fellow at American University's School of Law in Washington, DC. She's also a legal analyst for CBS News, and the author of How to Read the Constitution and Why," published last year by Harper Collins. She joins Tom from her office at American University.