“The Democratic-controlled legislature in Kennedy’s home state of Massachusetts in 2004 changed state law to require special elections and prevent then Gov. Mitt Romney, a Republican, from naming a replacement had Sen. John Kerry won the presidency.
Just days before his death Kennedy asked state lawmakers to revert to the old system so that the current Democratic Gov. Deval Patrick could name a successor if Kennedy had to leave office”
So, they change the law to prevent an unfair appointment (vs. elected) of a representative (a Republican) because it’s undemocratic… then want to change it back when they need an appointment of a representative (a Democrat) to try and push their bills through without bipartisan support.