A letter from federal health officials instructing states to be ready to begin distributing a vaccine by Nov. 1 — two days before the election — has been met, not with exhilaration, but with suspicion among some public health experts, who wonder whether the Trump administration is hyping the possibility or intends to rush approval for political gain. The skepticism comes amid growing questions about the scientific credibility of the FDA and the CDC, and their vulnerability to political pressure from President Donald Trump. Dr. Anthony Fauci … told CNN on Thursday that it is unlikely but “not impossible” that a vaccine could win approval in October, instead of November or December, as many experts believe.