[kinsman redeemer]

Here's another clue:

One suspect was allegedly plotting the attack while in a mental health facility, the sources added.

Or, to put it bluntly:

One suspect was allegedly plotting the attack is a Democrat, the sources added.

[tired&retired]

“One suspect was allegedly plotting the attack is a Democrat, the sources added.”

Probably the one in the mental institution... The staff registered and voted for him.