They should:

As long as we Communists are unable to take over state power and hold elections, with working people alone voting for their Soviets against the bourgeoisie; as long as the bourgeoisie exercise state power and call upon the different classes of the population to take part in the elections, we are in duty bound to take part in the elections with the purpose of conducting agitation among all working people, not only among proletarians. Lenin

It’s the most pragmatic way to continue the agitation. If Trump wins, it will become more difficult for socialists to gain entry into government.