WASHINGTON (AP) — President Donald Trump is facing a critical challenge as he tries to grapple with the new coronavirus outbreak: He must ask Americans to believe him even as he and some of his top advisers have contradicted government scientists in playing down the threat. The stakes for Trump are enormous, not simply from a public health and economic perspective but also for his credibility. As Americans prepare for what experts say is an inevitable outbreak in the country, the X-factor may be an unpredictable president who has clashed repeatedly with scientists in his own administration and tends to see any crisis through the lens of his own reelection chances.