The United States is hopelessly divided on taxes, spending, schools, guns, gay unions, drug legalization, medical care - you name it . The division is of course ultimately cultural, which means it is ultimately religious (culture/cultus = religion). If there were however two watershed issues that have led to the inability of our opposing politicians (and citizens) to talk to each other you would have to pick the Roe v. Wade decision and the 1987 nomination of Robert Bork to the Supreme Court. Jeffrey Rosen, then an aide to Sen. Joe Biden wrote in the New Republic, "Bork's record was distorted beyond all recognition... The borking of Bork was the beginning of the polarization of the confirmation process that has turned our courts into partisan war zones." That war has spilled across other political borders and now effects our national polity on a daily basis.
Why did Robert Bork provoke a scorched-earth reaction from the left? It probably comes down to his philosophy regarding original intent in the Constitution. "The truth is that the judge who looks outside the Constitution always looks inside himself and nowhere else. " - Robert Bork, died December 19th