There was some confusion as to which side was singing at first, with most people initially thinking it was the Republicans singing it as a goodbye to Obamacare.
"Na Na Hey Hey Kiss Him Goodbye" by Steam has a long history as a sports chant, as well as as a taunt in Congress. According to Talking Points Memo, Republicans sang it to Democrats after the passing of the 1993 Clinton tax bill.
Missouri Rep. Emanuel Cleaver told the Wall Street Journal it was a reference to the 2018 midterms and was not planned in advance.