Harry Truman manages a full-on UN victory in Korea, allowing him to win a landslide second term over Bob Taft in '52. Armed with a liberal Congress (one of the members of which is California Representative Ronald Reagan (D)), he passes single-payer health insurance and repeals section 14(b) of the Taft-Hartley Act, among other things. The Democrats hold on to the White House in 1956 with Vice President Scott Lucas, and are finally put out to pasture in 1960 with the election of Nelson Rockefeller as President.
Rockefeller oversees much of the Civil Rights movement in America. Re-elected thanks to a booming economy in 1964 over Democrat George McGovern, Rockefeller's Viet Nam policy is much more Eisenhower and a lot less Kennedy. The sixties see balanced budgets and small increases to social program funding, but never the Great Society bonanza of OTL. In 1968, voters choose Vice President Charles Mathias over Senator Robert Kennedy of New York in a tight election, despite Kennedy winning the popular vote.
By 1972, however, the impulse for social reform on the economic side of things is running over. President Mathias makes gestures toward reform, but his expansion of the war in Viet Nam, combined with an unfair draft system and student protests eventually leads to his downfall in 1972 to California's liberal Governor, Ronald Reagan.
As President, Reagan embarks on the 'decent society' program which enacts a flurry of economic reforms. A national industrial policy is implemented to help save American manufacturing, environmental policies are enacted to contain the growth of pollutants in products, and a system of national service is instituted to correct the unfairness of the existing selective service program. Reagan's Viet Nam policy leads to a negotiated peace, and South Viet Nam is essentially preserved in an OTL Korea-like fashion.
Reagan is re-elected in 1976 over Republican Senator George H. Bush of Texas. By 1980, the GOP has moderated their stance on economics a bit, and wins the White House with Massachusetts Senator Ed Brooke, the first African-American President.
As of 2011, American politics is quite different from OTL. The Democrats remain the nation's majority party, and unions and American manufacturing are as strong as ever. The Democratic Party of TTL has quite a few differences from that of OTL 2011, however. It is a multiracial party, but there are a lot less African-Americans and a lot more 'white ethnics'; Democrats do not have a strangle-hold on the nation's cities, and the party is a bit more socially conservative. Basically, think OTL's Labour Party in Britain (with authoritarian-ish sorts of policies with regard to law and order) but a bit more left-of-center ala the German SPD.
The Republicans are more or less where the British Lib Dems are today. Most are Rockefeller-esque Republicans with conservative fiscal views and somewhat centrist to left-of-center views on social issues. President Hillary Rodham (R-IL) recently left office after eight years of somewhat even economic growth and balanced budgets.