In the case of the supposed Nixon impeachment chatter, did the Senate have potentially 66 votes to impeach Nixon?
Simple answer? No.
In this period....1973 and 1974....the Democrats only controlled 56 of the Senate seats, with two independents, and the rest Republican (44).
Republicans possibly crossing over? No one has ever sat down and figured the real positions, and frankly....if you guess on this...you might have had five or six Republicans total....who would have gone with the Democrats.
This means Nixon would have survived the impeachment process? Yes. They would never reach 66.
But here's the thing....already in the first year of the administration, he was showing serious drinking issues, and he was probably not at the peak of his understanding or authority. It really didn't take much chatter to convince him to resign and step down.
Same issue with Clinton? Yes, they were never going to get to 66 Senators.
Trump? They might reach between 55 and 58 Senators total. Just something to think about.