anything. Bribery and treason are very specific crimes that would require proof of certain actions. Abuse of office is a huge umbrella that does not require proof of specific actions. The Dems will celebrate Festivus with the traditional airing of the grievances.
http://festivusweb.com/festivus-airing-of-grievances.php
There is no real burden of proof and they can use it to just public ally bash Trump.