The Presidency of Lyndon Johnson was perhaps the most pivotal of the 20th Century.
Scholars since have compared him to Ulysses Grant. No Lincoln (that comparison of course was reserved for Johnson's hero, Franklin Roosevelt), but a reformer who wanted to make sure that his reforms stuck.
So much so that he made sure to make his peace with the thoroughgoing conflict in Southeast Asia between the two Vietnams. Having adopted a strategy of counterinsurgency over the bombing program proposed by his generals, he was largely successful in cutting off the Ho Chih Minh trail.
Resupplying the South Vietnamese at that point, of course, was cake. The Republicans, though angry about the lack of "rollback" of communism, kept their mouths shut. Johnsonism was working quite well to quell the conflict. On the homefront of course, things were trickier. Johnson lost some support in the '66 midterms, though his masterpiece, the residential integration bill, made it out alive. The Freedom Budget too, with the tireless politicking of Martin Luther King Jr. and others like George Meany, would make it out of the dying gasps of reform as Johnson sought a second term in '68.
And he'd win it over Michigan Governor George Romney and George Wallace's dissident bid. Civil Rights, as it were, were here to stay. Johnson bequeathed the White House in 1972 to a pro-civil rights Republican, Chuck Percy as his Vice President Humphrey lost in a tight race. Percy's victory over Henry Jackson in 1976 and the subsequent election of Bobby Kennedy in 1980 brought the South back into the Democratic coalition. So long as anti-civil rights fits and starts were repudiated by both major parties, the South voted on pocketbook issues.
The West, however, would become a simmering pot of rebellion against further federal legislation to limit harmful economic activity. As white and black melded together, as both parties largely accepted the economic and social consensus of postwar liberalism, western conservatives organized and began to take over the Republican Party. Building upon the Goldwater movement, these conservatives rejected the idea of opposing civil rights (this had gotten them nowhere, fast) but instead pushed opposition to government expanditure with the social moderation of the Republicans.
The Republicans were out of power during the Kennedy (1981-1989) and Askew (1989-1993) years, but by 1992, western conservatism, so defeated since the 1960s, finally succeeded. President-elect George Deukmeijan might have failed to carry a single southern state (outside of Virginia, of course) but he'd locked up the west. And the selection of his running mate, Tom Kean, had helped eek out a razor-thin victory in the midwest.
As of 2012, with incumbent President Hillary Rodham, the Republicans have made the West their own, with proposals to reform immigration (to admit more immigrants, of course) and environmental conservation in addition to smaller government and the legalization of same-sex marriage. The Democrats, represented well in their 2012 failed nominee, former New York Senator Rudy Giuliani, have become a Southern-Midwestern-Northeastern party of labor and the multiracial working class.
There is some hope among Republicans that Texas, the home of LBJ and a Democratic stronghold, will soon be in contention for the GOP, thanks to demographic shifts and a high number of black suburbanites (who of course, have been shifting to the right eversince a majority of black Americans lived in the suburbs, or since 1990). President Rodham came close to picking off Texas in her re-election campaign against Giuliani, so anything seems possible going forward...