Do what you can, how you can. Disengagement is how entrenched powers win, more than insufficient force. Engagement sustains the activity necessary to feed all other forms of resistance.
A letter-writing campaign may not have the same effect as Green Mario or George Washington, but all forms of civic participation against tyranny count, in their own way - and not everyone should be expected to toss aside their lives and families at a moment's notice when other means of influence are still available.
Might suggest not wasting your time writing to GOP cretins, though.
When the great levee en masse of the French Revolution was called up, while soldiers were the primary need and request to the citizenry, all activity in service to the defense of liberty was required. Children were to collect cloth for uniforms; old folk were to preach resistance to tyranny on the street corners. Even in a time of literal war, there are other forms of resistance that are respectable and helpful.