Yes the Senate should call witnesses with FIRST HAND KNOWLEDGE of what Trump was doing with Ukraine and the financial support that was being held as well as the OVAL OFFICE meeting that Zelinski wanted. As for those of you saying the Senate should not call any witnesses that the House didn't call. Maybe you should stop reading Bretbart, Fox Entertainment and other far right so called news outlets and actually do some actual research on what is going on. Bolton, Mulvany as well as other top officials at the White House were subpoenaed and refused to appear before the House Committees. The reason the House decided not to take it through the courts, is 2 fold. 1. in 1974 (during the Nixon Impeachment) the Supreme Court ruled that the President couldn't invoke Executive Privilege to block Congress from doing it's Constitutional Duty. 2. Due to the severity of the case and the time constraints due to the 2020 Presidential Election, they felt running the subpoenas through the courts would take to long and could drage the Impeachment Hearings till after the election. And, if Trump were to be voted out of office, it would make impeaching him for them, impossible as he would no longer be President.