Facts speak for themselves.
The Democratic Party under Barack Obama in 2010 suffered the greatest defeat for a newly elected president in a midterm since the Republican Party under Warren Gamaliel Harding in 1922. Democrats, at this writing, dropped 61 seats in the House of Representatives, where they will now be in the minority, and 6 seats in the Senate, where they will continue to hold a slight edge. The Democratic defeat was historic by other measures as well--in House seats lost in a congressional election (the most since 1948), and in House seats lost in any midterm (the most since 1938). But it is the performance of a president's party following his first election that is the relevant point of comparison today.
The midterm election is one of the distinctive features of America's constitutional system. By allowing for an expression of voter sentiment separate from the selection of the president, midterms help supply the concrete political support in Congress for checking presidential programmatic power. A check of this kind seems to be exactly what the public had in mind in 2010, ending liberal hopes that Obama's presidency would inaugurate a "new" New Deal.