While there are many reasons for the slowness of the institutional response in the political system to Trump, one actually can be fixed quite easily.
Right now, the press are energized, the courts seem to be standing up for judicial supremacy, and the investigatory agencies are still able to get the most disturbing facts before the public.
The problem is that there is no truly independent set of investigations going on, because of the Republican failure.
The simple solution is for three or more senators to shift parties for the purpose of establishing the appropriate investigatory process. Such a switch, perhaps by McCain, Lindsey and one more, could be limited to the organization of the Senate, and the Rs could still vote with their colleagues on all substantive matters if they wished. Those three would have to expect to be primaried, but who knows, by the end of this they might be the safest Republican senators.
Anyway, just the threat of this should be enough to get McConnell to back down, set up a true investigation, and allow it to go wherever it goes. The tax returns alone might be enough.