The famously fractious party that tore itself apart in the 1960s and 1970s over civil rights and the Vietnam War, that lost a series of blowout presidential elections in the 1980s and painfully reinvented itself in the 1990s, faces little of the infighting or self-doubt that for decades seemed as much a part of being a Democrat as worshiping FDR or watching the South, a former party bastion, inexorably slip away.