President Joe Biden told congressional Democrats in a letter on Monday that he will continue his reelection bid despite mounting concerns about his mental fitness and the viability of his campaign, while also hitting back at party “elites” in an interview ahead of a critical week on Capitol Hill. “I want you to know that despite all the speculation in the press and elsewhere, I am firmly committed to staying in this race, to running this race to the end, and to beating Donald Trump,”...