This is a great question and one that has perplexed me for decades. Look at what Harry Reid did with the Senate Nuclear option. Before that there was the Biden Rule on Supreme Court picks. They do these radical things for immediate benefit and then scream bloody murder when the Republicans turn the tables on them using the very policies and precedents that they started.

I think the difference today is that the mainstream media used to be the power that kept political power in check for blatant hypocrisy. Now the Dems know they can go scorched earth and get cover by the media, and if the GOP tries the same the media will go scorched earth on the GOP.

My perspective is that we finally met the enemy, and it is our media.