I am haunted by the death of democracy in 1930s Japan, as America faces an escalating wave of exhortations toward violence from the progressives that dominate our institutions of culture.  In the run-up to World War II, fanatics organized a wave of assassinations that simply killed off politicians who stood in their way, ending an already shaky democracy.  This period is commonly known among historians as "government by assassination."  They may have been militarists, but like all true fanatics, they were serving a cause so holy and so pure in their version that any and all means necessary were justifiable in their fevered minds.

Austin Bay points out at The American Spectator that, had optimal conditions (from James Hodgkinson's perspective) prevailed:

[He] could have killed 32 Republican members of the House and two Senators. ...

Killing 32 Republican members of the House reduces the Republicans to 207 seats. That means the nation must conduct 32 special elections. That means the Resistance (which includes Hillary Clinton) has 32 opportunities to seize a Republican seat in a special election. ...

Agreed, murdering two Republican Senators doesn't shift power in that chamber, but it also necessitates two special elections where – in the hate-filled Occupy Whatever brain of a Hodgkinson – a Democrat might replace a Republican.

Flipping the House makes Nancy Pelosi the Speaker, and gives her the votes to impeach Donald Trump. Once the House impeaches the President, in a 50-50 Senate two or three "Never Trump" Republicans might vote to convict and remove him!

Check the terrorist's math. Subtract Republicans, then add Democrats.

Even if Hodgkinson didn't see this possibility with clarity, his murder spree had this evil potential. 

The problem is that there are lots of deranged people out there on the left today who can be termed fanatics if the definition includes fighting against an ultimate evil or for an ultimate cause.  Trump Derangement Syndrome is a mass phenomenon, and it is actively being fanned by powerful forces.  How many disturbed people can be pushed over the edge to engage in a wave of killing?  How many do you need?

I have to presume that the FBI and other agencies are tracing the entire electronic network of communication connected to Hodgkinson.  That list he carried could mean he was part of a larger group, assigned to take out a certain set of GOP leaders, but that is only a possibility, and if this is being pursued, we will not hear about it.

I am less concerned about an organized plot against the GOP than I am about random fanatics acting out, convinced they are doing the right thing by all the cultural cheerleading for violence.