It is an irony, but not a coincidence, that Barack Obama’s post-partisan era has seen the rise of the Tea Party movement and Occupy Wall Street.

Certainly, the momentum of polarization was strong before Obama arrived in Washington. Over the past few decades, Republican and Democratic congressional delegations have been churned into ideological homogeneity. Members seem to inhabit not different parties but different planets. The number of Americans who call themselves moderates has declined, while the number of people identifying themselves as conservatives or liberals has increased. Both sides find their beliefs reinforced by partisan media, for whom ideology has become a marketing tool. Every ideological slight — every Nazi comparison, every intemperate comment by a pastor or union leader — is elevated into a national controversy. The Internet and cable news have become an endless buffet, feeding the outrage of a nation.

But far from halting or reversing these trends, Obama has worsened them — setting the stage for the most polarized election of recent history.

His failure has generally been not a matter of tone but of policy. The president’s early post-partisan rhetoric was never matched by innovative ideas that crossed ideological lines and created coalitions. Bill Clinton had welfare reform. George W. Bush had No Child Left Behind. Obama, in contrast, pursued a liberalism both bold and uncreative — a massive Keynesian stimulus, a brand-new health entitlement, the largest deficits in American history.

Congressional Republicans were obstructionists — but often because Obama’s aggressive, ideological power play made obstructionism identical with Republicanism. GOP members could not accept an ambitious expansion of the size and role of government without surrendering their identity. Some in the Republican Party have enjoyed their role in opposition too much. But they were given few incentives to temper it.

The public response ran in parallel — a Tea Party revolt and a near-landslide Republican midterm election. Liberal accusations that this reaction was artificial, irrational or race-based only fed the polarization. In typical fashion, many offended conservatives have also engaged in ideological overreach, calling for a government cut to the size of an 18th-century agrarian republic.

Feeling provoked himself, Obama has now abandoned the pretense of post-partisanship. He runs for reelection on the platform of funding unreformed entitlements with higher taxes on the wealthy. It is hard to imagine a more typical, tired, polarizing Democratic message. It is a surrender to predictable national division.

There are some who stress the positives of polarization — that it encourages conviction, participation and clear political choices. The defense of partisanship is oddly bipartisan. It can be heard among activists at Tea Party rallies and in New York’s Zuccotti Park.

But polarization complicates the task of governing. A highly partisan majority — as Obama proved during his first two years — can get things done. It just can’t get the most important things done. For America to remain a competitive economic power, the president and legislature need to undertake a series of complex, controversial reforms of the tax code and entitlement system. This will be hard enough without the cultivation of ideological rigidity and mutual disdain.

A partisan populism has its virtues and uses. But it would do little good to ask a delegation from the Tea Party and one from Occupy Wall Street to meet in a room and hammer out an entitlement reform package. The hammers would be used for different purposes. Our urgent need is not for politicians who reflect partisan passions but for officials willing to risk partisan wrath in pursuit of the public good.

This message is properly directed at both parties. But Obama’s embrace of unreconstructed liberalism ultimately hurts his party more. For a variety of historical reasons, the Democratic Party is more ideologically diverse than the GOP. While about 40 percent of Democrats identify themselves as liberals, more than 70 percent of Republicans call themselves conservatives. So when Obama channels the spirit of LBJ — or when Occupy Wall Street protesters are embraced as Democratic poster children — the risks of division within his political coalition are serious. Democratic candidates in places such as Missouri, Nebraska, Louisiana or Montana are forced to distance themselves from national Democratic ideology on tax increases and the expansion of government. When Obama whips up the liberal base to serve his political interests, it betrays a number of Democrats down the ticket.

It also betrays the appealing, unifying candidate who ran in 2008. We are being asked to reelect a political figure who no longer exists.

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