The Murder of Mr. Smith(Sr?)
A sub-subplot of the film is the implied murder of Jefferson Smith's father.
What we know:
Paine & Mr. Smith Sr. were friends
Mr. Smith Sr. was a Journalist
The Taylor Machine tried to control every press in the state.
Paine reacted with shock and emotion when he is reminded of Mr. Smith's murder & Taylor's willingness to use violence to control the presses.
It seems logical that Taylor may have had some kind of connection with the murder of Smith's father and if this were a subplot it would help explain the irrational and possibly illogical actions Paine is willing to take as he is forced to insult and attack Jeff and afterword.
However as a literal work it would be far more interesting if rather than Taylor it was a Smith Machine, Perhaps Mr. Smith Sr would have lost his idealism grew into a tyrant.