in the end, it's a failure to have an informed, interested electorate

"GOP senators and aides were confident that voters were paying little attention based on a survey conducted by the National Republican Senatorial Committee, the official campaign arm of Senate Republicans."

also a willingness to buy completely bogus arguments. basically: the president can do anything he wants if he thinks it's in his personal interest, because that's in the national interest (quid pro quo is not impeachable):

"Even if Bolton’s allegations of a quid pro quo were true, isn’t that still not an impeachable offense, so would his testimony add anything? Patrick Philbin, a deputy White House counsel, responded that it would not be an impeachable offense. That answer was pivotal, especially in getting Lisa’s vote,” Cruz said."

"I decided to go through all 10 analysis sections to decide for myself. And I found that, in five of the 10 areas, Mueller seems to believe that all three criteria to charge a crime are supported by evidence.

1. Trump’s conduct toward Paul Manafort’s cooperation
2. Efforts to have Donald McGahn deny that Trump tried to fire Mueller
3. Efforts to curtail the Mueller probe
4. Efforts to fire Mueller
5. Conduct involving Michael Cohen"