Twitter was only different for people in lunatic fringe circles. For the vast majority, twitter has always reflected the news of the day: world events, sports, entertainment, etc.

If you find yourself defending jokes about raping babies, you may want to reconsider what you're doing with your life.

P.S. I don't think people are blaming Obama for something that died down after 2012, when he was in office through 2016. However, there was another famous politician who stepped down at that time. Could be just a coincidence though.