He brought the crowd together, incited them with fiery rhetoric and lies, and then directed their anger in one direction. When all hell broke lose, he did not do a single thing to try and put a stop to the violence. It took 2hrs to hear a statement from the POTUS asking his supporters to go home, and over 24hrs for him to condemn the actions.Legally, he did not incite violence, so any impeachment would be, once again, purely political.
That is a failure of leadership, and a failure to discharge his duties as POTUS. The 25th amendment is more appropriate given these facts, but since Pence does not wish to do it then it is up to Congress to pick up the ball and go with it.