IN 2008, Barack Obama’s presidential campaign seemed to rewrite all the rules in electoral politics and herald a new progressive era in America. Democrats assembled a huge Congressional majority and, in the euphoria that followed the historic election, were poised to enact sweeping change. However, despite some notable successes  the stimulus package, health care reform, tighter rules for the financial industry  things have not gone according to plan. Just two years later, Democrats face a bad economy, a skeptical public, a re-energized Republican Party and a coming avalanche of losses in the midterm elections.

What happened? One important explanation is that divisions inside the Democratic coalition, which held together during the 2008 campaign, have come spilling out into the open. Conservative Democrats have opposed key elements of the president’s agenda, while liberal Democrats have howled that their majority is being hijacked by a rogue group of predominantly white men from small rural states. President Obama himself appears caught in the middle, unable to satisfy the many factions inside his party’s big tent.

Conservative Democrats in the House of Representatives  whose election in 2006 and 2008 enabled Nancy Pelosi to preside over a supermajority (there are 255 Democrats and 178 Republicans)  increasingly question whether she should relinquish her position as speaker. Representative Heath Shuler of western North Carolina, a leader of the restive Blue Dog Coalition of Democrats, has even hinted that he may run for her job. Representative Shuler is an unlikely candidate for leader of the party  a devout Southern Baptist who voted against the stimulus, the bank and auto bailouts and health care reform. Yet he’s exactly the kind of Democrat that the party worked very hard to recruit for public office.

In 2005, Howard Dean, who was then the chairman of the Democratic National Committee, carried out a campaign to elect as many Democrats as possible. In long-ignored red states, both Mr. Dean and Rahm Emanuel, then the chairman of the Democratic Congressional Campaign Committee, backed conservative Democrats who broke with the party’s leadership on core issues like gun control and abortion rights. Mr. Shuler was one of Mr. Emanuel’s top recruits. The party leaders did not give much thought to how a Democratic majority that included such conservative members could ever effectively govern.