Trump won #EliseStefanik's district by more than 20 points. Now Trump is so worried that if she leaves #Congress to accept the nomination to be UN Ambassador Republicans could lose the special election to replace her. Given the polling plus the reality of who votes in special elections (highly motivated, highly educated voters) I suspect this fear is not unwarranted.
On the one hand this is encouraging because it shows republicans have internal polling that has them legitimately worried.
On the other hand it sucks that Trump was savvy enough to pull Stefanik's nomination. Losing a congressional election in such a safely red district would send an enormous shock wave through the entire US Congress that would cause a lot of them to grow a spine, because the voters would have made it crystal clear that a lot of "safe" republican seats are now tossups and the members need to adjust their activity accordingly.