Dr. Anthony Fauci is returning to Capitol Hill at a fraught moment for the nation’s pandemic response. Coronavirus cases are rising in about half the states and political polarization is competing for attention with public health recommendations. The government’s top infectious disease expert is testifying Tuesday before a powerful House panel, along with the heads of the Centers for Disease Control and Prevention and the Food and Drug Administration. The nation is emerging from weeks of stay-at-home orders and business shutdowns. But that’s being done in an uneven way, with some states far less cautious than others.