It's no coincidence that conservative former Rep. Pat Toomey of Pennsylvania is mulling a repeat of his 2004 Republican primary challenge to Sen. Arlen Specter at the same time that liberal activists and bloggers have launched an organization to mount primary contests against congressional Democrats who deviate from the party line too often.

For a moment, President Obama's election around themes of national reconciliation seemed to suppress the militant voices dubious of any compromise between the parties. But now, Washington's ideological enforcers -- the most strident talk-radio hosts and bloggers, the vanguard interest groups of left and right -- are reasserting themselves. At a precarious time, that's a dangerous development.

After the bruising stimulus fight, too many in Congress are retreating to old battle lines and abandoning the hard work of outreach.

The magnitude of the problems we face and the ambition of Obama's responses to them guarantee sharp debate between (and within) the parties. That's entirely appropriate. What's ominous, though, is the intensifying drive from left and right to systematically widen the distance between the sides -- and punish anyone trying to bridge it.

That instinct infuses the denunciation of the three Republican senators who provided the decisive votes for Obama's stimulus plan -- Specter and Maine's Susan Collins and Olympia Snowe. The Club for Growth, a conservative anti-tax group headed by Toomey, labeled the trio their "Comrade of the Month," as if voting for the stimulus package, after forcing concessions, revealed them as closet Marxists. One day earlier, Toomey announced he was considering a rematch against Specter.

Whether or not Toomey eventually runs, his threat appears designed to discourage GOP moderates from supporting Obama too often. Giving in to such threats could prove stunningly counterproductive for Republicans. Obama won Pennsylvania by 620,000 votes; the Democrats' best chance of beating the resilient Specter is to tar him as an obstacle to the president. The more Specter drifts right to pre-empt a primary challenge, the more he'll validate that attack in a general election campaign. And although Toomey is talented, if he defeats Specter by promising unremitting opposition to Obama, the Democrats' chance of capturing the seat will soar.

Moderate congressional Republicans from coastal states resistant to doctrinaire conservatism have been routed at the polls in recent years, partly because the Right's demand for unwavering fealty has forced them to constantly choose between antagonizing their base and alienating swing voters. The GOP has purchased uniformity at the price of contraction. Because enforced ideological conformity has worked so well for Republicans, the Left has chosen this moment to try to impose its own version on Democrats. In late February, a coalition of prominent liberal groups and Internet activists formed an organization to fund primary challenges to congressional Democrats who break too often from the party consensus.

This is as myopic as the Republican attacks on moderates. The Accountability Now PAC hopes to pressure moderate or conservative Democrats into supporting all of Obama's agenda. But if Obama's program can't hold most of those swing-district Democrats, it's probably a sign that he is also losing the center of the country. More often than not, ousting these Democrats would amount to shooting the messenger.

Across many fronts, Washington's centrifugal impulse is resurfacing. After the bruising stimulus fight, too many in Congress are retreating to old battle lines and abandoning the hard work of outreach. Liberal groups are firing invective at the health insurance industry even though it has signaled important flexibility on reform. Rush Limbaugh has declared he wants the president to "fail," and Democrats, including the White House, have manufactured a silly controversy over whether the strutting Limbaugh wears the GOP crown.

This might be amusing in other circumstances. But at this daunting moment, trivial bickering and demands for absolutism are indulgences the country can't afford. Obama passed his stimulus plan over virtually unanimous Republican opposition, but the people will be better served if both parties and a broad range of interests contribute to solutions on big problems such as health care, energy, and stabilizing the financial system. In this emergency, Obama has a responsibility to reach out. And his critics have an obligation to reach back. That's less likely as long as ideologues on each side attack all concession as capitulation.

Americans would not tolerate leaders who refuse to come together during a national security crisis. We should accept no less cooperation in the economic crisis that is now menacing American families as much as any threat from abroad.

This article appeared in the Saturday, March 14, 2009 edition of National Journal.

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