Writing in New York magazine, Jonathan Chait offers a plausible explanation for the Republican leadership’s increasingly hysterical rhetoric — panic about demographic transformation:

…The modern GOP–the party of Nixon, Reagan, and both Bushes–is staring down its own demographic extinction. Right-wing warnings of impending tyranny express, in hyperbolic form, well-grounded dread: that conservative America will soon come to be dominated, in a semi-permanent fashion, by an ascendant Democratic coalition hostile to its outlook and interests. And this impending doom has colored the party’s frantic, fearful response to the Obama presidency.
The GOP has reason to be scared. Obama’s election was the vindication of a prediction made several years before by journalist John Judis and political scientist Ruy Teixeira in their 2002 book, The Emerging Democratic Majority. Despite the fact that George W. Bush then occupied the White House, Judis and Teixeira argued that demographic and political trends were converging in such a way as to form a ­natural-majority coalition for Democrats.

As for the key particulars of the demographic transformation, Chait observes,

…As a whole, Judis and Teixeira noted, the electorate was growing both somewhat better educated and dramatically less white, making every successive election less favorable for the GOP. And the trends were even more striking in some key swing states. Judis and Teixeira highlighted Colorado, Nevada, and Arizona, with skyrocketing Latino populations, and Virginia and North Carolina, with their influx of college-educated whites, as the most fertile grounds for the expanding Democratic base.

Chair believes the demographic dynamics were the real driving force behind the Obama phenomenon, not just his charisma.

…Above all his sweeping win reflected simple demography. Every year, the nonwhite proportion of the electorate grows by about half a percentage point–meaning that in every presidential election, the minority share of the vote increases by 2 percent, a huge amount in a closely divided country.

He argues that even Dukakis could have won in 2008, as a result of demographic change. He cautions, however, that the changes don’t necessarily translate into a permanent Democratic advantage because “eventually the minority learns to adapt to an altered landscape.” In addition, short term “shocks” like scandal, recession or war can reverse demographic advantages.
Chait adds that the tea party and the “apocalyptic rhetoric” are symptomatic of the panicked response of both conservative leaders and voters. He adds “What’s novel about the current spate of Republican millennialism is that it’s not a mere rhetorical device to rally the faithful, nor even simply an expression of free-­floating terror, but the premise of an electoral strategy.”
He believes it also explains the over-the-top voter suppression surge of the last three years.

None of this is to say that Republicans ignored the rising tide of younger and browner voters that swamped them at the polls in 2008. Instead they set about keeping as many of them from the polls as possible.The bulk of the campaign has taken the form of throwing up an endless series of tedious bureaucratic impediments to voting in many states–ending same-day voter registration, imposing onerous requirements upon voter-registration drives, and upon voters themselves. “Voting liberal, that’s what kids do,” overshared William O’Brien, the New Hampshire House speaker, who had supported a bill to prohibit college students from voting from their school addresses. What can these desperate, rearguard tactics accomplish? They can make the electorate a bit older, whiter, and less poor. They can, perhaps, buy the Republicans some time.

The 2012 election, Chait believes, is likely the GOP’s “last chance to exercise power in its current form, as a party of anti-government fundamentalism powered by sublimated white Christian identity politics. (And the last chance to stop the policy steamroller of the new Democratic majority.)” As desperate as the GOP strategy appears, the stakes are more than a little daunting for Dems, as Chait explains:

…If they can claw out a presidential win and hold on to Congress, they will have a glorious two-year window to restore the America they knew and loved, to lock in transformational change, or at least to wrench the status quo so far rightward that it will take Democrats a generation to wrench it back. The cost of any foregone legislative compromises on health care or the deficit would be trivial compared to the enormous gains available to a party in control of all three federal branches.

In short, either way, 2012 will be one of the most consequential elections since FDR’s 1932 victory. If any Dems needed a reason to go all in on re-electing the President, Chait’s article explains it well.