We’ll see how Obama’s vast plans play out. We’ll see what unexpected nightmares, bigger than the swine flu, materialize on his watch. The 100 Days celebrations could not fade soon enough, because neither he nor the country should be lulled into resting easy. There are at least two toxic fiefdoms to keep the president and us awake at night: Pakistan and Wall Street. Both could wreak further untold catastrophe. Obama has control over neither, and in the case of the financial sector, he is fielding a team dominated by Robert Rubin protégés whose wisdom remains, to put it generously, unproven.

But if those are the obvious hotspots for this presidency, there is also the domestic political culture to worry about. The Republican Party has collapsed, and that is not a good thing for the country or for Obama. We need more than one functioning party, not just to ensure checks and balances and pitch in ideas at a time of crisis, but to temper this president’s sporadic bursts of overconfidence and triumphalist stagecraft. No one is perfect. We must remember that there is also an Obama who gave us “You’re likable enough, Hillary,” a faux presidential seal and a convention speech delivered before what Sarah Palin rightly mocked as “Styrofoam Greek columns” hauled out of a “studio lot.”

That Obama needs a serious counterweight in the political arena. But the former party of Lincoln and liberty has now melted down to a fundamentalist core of aging, rural Dixiecrats and intrusive scolds  as small as 20 percent of the populace in the latest polls. Its position on the American spectrum of ideas is somewhere between a doomsday cult and Scientology.

Image Frank Rich Credit... Fred R. Conrad/The New York Times

Arlen Specter’s defection is the least of the Republicans’ problems, a lagging indicator. Though many characterize his departure as a “wake-up call” for the party, it’s only the most recent of countless wake-up calls the party has slept through since 2006. That was the year that Specter’s Pennsylvania Republican colleague in the Senate, Rick Santorum, lost his seat by a margin of more than 17 percentage points. Despite that rout and many more like it of similar right-wing candidates throughout America, the party’s ideological litmus test is more rigid than ever. The G.O.P. chairman, Michael Steele, and enforcers of Republican political correctness like William Kristol and the blogger Michele Malkin jeered Specter and cheered his departure. A laughing Limbaugh seconded e-mail from listeners commanding Specter to “take McCain with you  and his daughter.”

You can’t blame the president if he is laughing, too. As The Economist recently certified, the G.O.P. is now officially in the throes of “Obama Derangement Syndrome.” The same conservative gang that remained mum when George W. Bush praised Putin’s “soul” and held hands with the Saudi ruler Abdullah are now condemning Obama for shaking hands with Hugo Chávez, “bowing” to Abdullah, relaxing Cuban policy and talking to hostile governments. Polls show overwhelming majorities favoring Obama’s positions. But his critics have locked themselves in the padded cell of an alternative reality. Not long before The Wall Street Journal informed its readers that 81 percent of Americans liked Obama, Karl Rove wrote in its pages that “no president in the past 40 years has done more to polarize America so much, so quickly.”

From derangement it’s a small step to madness. Last week, the president of a prime G.O.P. auxiliary, the Concerned Women for America, speculated that the president’s declaration of “a state of emergency about the flu was a political thing” to push through Kathleen Sebelius’s nomination as secretary of health and human services. At those tax-protesting “tea parties” on April 15, signs and speakers portrayed Obama as a “fascist,” a “socialist,” a terrorist and Hitler. Republican governors have proposed rejecting stimulus money for their states (only to fold after constituents rebelled) or, in the notorious instance of Rick Perry of Texas, toyed with secession from the union.