Boise Mayor Lauren McLean was so sure that dark money operatives would buy televisions ads for her election bid last year that she didn’t buy any herself. Her campaign spent a few grand on Facebook and Google ads, but most of her $355,000 budget went to the practical expenses of running her 2019 campaign: staff, printing, mail, food, and related items. On paper, she had around $100,000 less than her opponent, fellow Democrat and —at 16 years in office — Boise’s longest-serving mayor, Dave Bieter. But operating mostly off the books, a shadow campaign sent $310,000 in-state to blanket Boise...