Ramesh Ponnuru says that the restrictionist campaign to defeat Chris Cannon worked this time because “the restrictionist winner did not run as a single-issue candidate.” That’s certainly part of it — a single-issue candidate can make a splash running on border security or immigration policy more generally, but even voters who care deeply about immigration want a congressman who seems interested in other things as well. A monomaniacal focus on immigration isn’t usually an election winner. But I’d also point to the professionalism of the candidate: a lot of single-issue candidates tend to be objectively bad candidates in other respects, as fanaticism isn’t an appealing trait. Tom Tancredo’s immigration positions have more support than his amateurishly run presidential campaign. Chaffetz won in no small part because he was a serious candidate who ran a competent campaign that paid the right amount of attention to the incumbent’s unpopular immigration record.