Ken Eichstaedt, an unlikely politician, felt nervous the first time he knocked on doors in his hunt for votes in Novato. Would people give time to a West Marin water board candidate, a relative unknown from the far side of the district? Would they slam the door in his face?

The doormat at one house was not encouraging. “Don’t come knocking unless you got a warrant,” it said.

Mr. Eichstaedt, an engineer who lives in…