Honestly, it's the best move he could have made.

He needed to end the investigation to save face and prevent more indictments of his allies. He's not actually firing Mueller. He's got plausible deniability. Plenty of liberals hate Sessions. Now, the investigation is to be killed slowly and quietly. He gets to say it's because it's costing too much money. He gets to claim it's a witch hunt even more when it can hardly function due to lack of a budget. If people leak, he gets to have his new AG fire them and/or press charges for releasing classified information.

Mueller and his team are law abiding citizens. Trump is up the chain of command. If they're given an order, they'll have to take it. They won't break the law.

And now, since the investigation will slowly die, so will the outrage.

Something needs to happen soon, or nothing will happen at all.