Nevada’s Democratic political machine was held up as a model for other states where neither party has consistently dominated. But it was a machine built for another era.

Its success relied on hundreds of people knocking on thousands of doors for face-to-face conversations with voters. Now, there are fewer than half as many people canvassing for Democratic voters as there were in September 2016. And some Democratic strategists warn that Nevada could be in 2020 what Wisconsin was in 2016 — a state that the Democrats assume is safely in their column but that slips away.

“I am saying every day: We are more vulnerable than you think we are,” said Annette Magnus, the executive director of Battle Born Progress, a liberal group that has yet to raise enough money to start the kind of campaigning this fall that it has previously deployed. “We frankly need to fire up our base a little more, and we have so much work in front of us. Nevada does not have the resources we need to do that yet.”