Nathan Hatcher, a Republican volunteer in the Denver suburb of Arvada, said that heavy outside spending in Colorado this year has overwhelmed traditional neighbor-to-neighbor outreach.
Outside groups flood Colorado with ad money →
"These ads, they scare people," Mr. Hatcher said. "One of my daughter's friends was talking about one of these ads, and she's 12. I mean, what is going on? It's both sides doing it, and it seems like there's no way to stop it."