In a two party democracy, the major parties are inevitably coalitions of disparate groups, not ideologically pure or monochromatic. From the 1930s to the 1970s Democrats dominated national politics due to the power of the so-called New Deal coalition, an unlikely combination of Southern whites, educated liberals, African-Americans, and blue collar workers.
Richard Nixon's landslide victory in 1972 pointed to the fragility of that coalition, which was definitively broken apart after Reagan's victory in 1980. Nixon is known for his rhetoric about the "Silent Majority," which he also termed the "New American Majority." He skillfully courted the unions, Southern whites, the suburbs, and urban white ethnics so crucial to his crushing victory in 1972. To do so, Nixon exploited the fears of those who were confused or angry about the changes of the 1960s, and who resented the counterculture, war protestors, and growing racial equality. Others have noted that the Republican party has increasingly become a white people's party, that trend stretched back to Nixon's "Southern Strategy" and the ways Republicans threw their doors open to the likes of Strom Thurmond and Jesse Helms.
Back then, the racial demographics were firmly on the Republicans' side. If they were going to win a majority of white people, they would likely win the presidential election. Reagan knew this too, hence his defense of "states rights" in 1980 in Mississippi and constant talk of "welfare queens" driving Cadillacs during that same election. By that time evangelicals too had entered the fray as a newly powerful force for conservatives. Calls for low taxes, flag waving, "law and order," and "family values" combined to give conservatives at least one issue that appealed to a great number of the white voters who were once loyal Democrats who might not have bought into the supply side snake oil.
It appears nowadays that just as the Democrats lost their coalition, the Republicans are losing theirs, too. One reason, of course, is that the country is much less white than it used to be. This change has been used to powerful effect to whip up Tea Party resentment against president Obama, but will be a diminishing return because the audience for this rhetoric is getting older and older. Some Republicans are smart enough to realize this, and are desperately pushing forward not ready for prime-time (but brown-skinned) pols like Jindal and Rubio, and are backing immigration reform to court the Latino vote. Their Tea Party base, intent on xenophobia, is not letting the savvier heads get their way. Romney won a majority of white voters (including white women), but still lost the election very definitively.
Other factors are under-cutting the old majority as well. By obsessing over ideological purity, Republicans are making it difficult to build a broad coalition in the first place. The GOP's need to placate its religious wing is increasingly alienating younger voters who are much more secular than their forebears. That trend will only continue. Many of the social issues they used to peel off Democrats in the past, such as abortion, gay rights, drugs, and narrowing the church-state separation are no longer as potent, and actually work against conservatives. In essence, the culture wars are backfiring on their biggest warriors. Last, the growth of cities and decline of suburbs, as well as the changing demographics of suburbs are working against conservatives, not to mention that rural America has entered permanent decline.
The question is whether Republicans can fight a rearguard action to avoid becoming a marginal, white/rural/Christian identity-politics party buoyed by corporate dough. One thing that now is clear is that the coalition that had been so successful for conservatives going back to Nixon is breaking apart and dwindling in number. Maybe, just maybe, a major political sea change is in the offing.