In the past four decades, the two political parties have become more internally homogeneous and ideologically distant. In “The Audacity of Hope,” Obama wrote longingly about American politics in the mid-twentieth century, when both parties had liberal and conservative wings that allowed centrist coalitions to form. Today, almost all liberals are Democrats and almost all conservatives are Republicans. In Washington, the center has virtually vanished. According to the political scientists Keith T. Poole and Howard Rosenthal, who have devised a widely used system to measure the ideology of members of Congress, when Obama took office there was no ideological overlap between the two parties. In the House, the most conservative Democrat, Bobby Bright, of Alabama, was farther to the left than the most liberal Republican, Joseph Cao, of Louisiana. The same was true in the Senate, where the most conservative Democrat, Ben Nelson, of Nebraska, was farther to the left than the most liberal Republican, Olympia Snowe, of Maine. According to Poole and Rosenthal’s data, both the House and the Senate are more polarized today than at any time since the eighteen-nineties.
The Obama Memos: How Washington Remade the President : The New Yorker
