Janesville, Wisc.

At a rally here Saturday afternoon, tens of voters thronged to hear Paul Nehlen’s closing arguments. Although the state’s GOP primary is Tuesday and he’s bidding to upset the sitting speaker of the House, only about 100 people showed—despite the luminaries who traveled to this southeast Wisconsin district on Mr. Nehlen’s behalf, such as the performance artist Ann Coulter and film director Ron Maxwell, whose credits include “The Parent Trap 2” (1986).

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