Single-issue restrictionists have tried to unseat Rep. Chris Cannon in primaries before, and lost. High-immigration Republicans have on each of those earlier occasions said that the results showed that restrictionism has no political power. My theory has always been that single-issue campaigns based on restrictionism are unlikely to work almost anywhere–but that restrictionism could help a candidate with a larger platform.
A number of things were different this time, starting with the public mood toward incumbent Republicans. But it also appears that the restrictionist winner did not run as a single-issue candidate.
UPDATE: James Antle adds, “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.”