I'm going to guess this is the Trump effect at work - he endangers quite a few house incumbents, some not even close to vulnerable in past elections like Issa or Petersen, but in the process saves a few like Blunt, Katko, and Poliquin.
Trump isn't gonna save Blunt (I'd argue he hurts him by bringing out some blue-dog DINO types who will still vote for Kander), Katko is simply a strong incumbent facing a weak opponent, and Poliquin – while probably helped by Trump – would likely be losing if he were facing someone like Troy Jackson or Joe Baldacci.
