NEO: A history of partisanship in US presidential impeachments.
The Founders were fearful that impeachment would become a partisan endeavor, and they were right to be fearful. It has. That’s why the Founders set the bar so high for a Senate conviction.
If you look back on the history of US presidential impeachments, you will find a great deal of partisanship in the support for impeachment and removal, except for the impeachment that didn’t happen: that of Nixon, whose opposition was so bipartisan that he realized Senate conviction was likely and he stepped down before the impeachment ever occurred.
You will also find that the majority of the bipartisanship and/or crossing of party lines was by Republicans rather than Democrats, and it was Republicans voting against impeachment and/or removal of a Democrat president. This will probably not be a surprise. Democrats tended much more to vote as a bloc for impeachment and/or removal of a Republican president.