Senator Christopher S. Murphy, an ambitious young Democrat from Connecticut, went on television on Sunday with a carefully worded warning to President Biden about the viability of his campaign. “This week is going to be absolutely critical; I think the president needs to do more,” Mr. Murphy said, arguing that Mr. Biden needed to hold a town hall and participate in unscripted events because “the clock is ticking” for him to put to rest the doubts about his candidacy raised by a disastrous...