As a lifelong Democrat, I have a mental picture these days of my president, smiling broadly, at the wheel of a speeding convertible. His passengers are Democratic elected officials and candidates. Ahead of them, concealed by a bend in the road, is a concrete barrier.

They didn't have to take that route. Other Democratic presidents have won bipartisan support for proposals as liberal in their time as some of Mr. Obama's are now. Why does this administration seem so determined to head toward a potential crash and burn?

Even after the embarrassing playout of the Obama-invented Great Sequester Game, after the fiasco of the president's Fiscal Cliff Game, conventional wisdom among Democrats holds that disunited Republicans will be routed in the 2014 midterm elections, leaving an open field for the president's agenda in the final two years of his term. Yet modern political history indicates that big midterm Democratic gains are unlikely, and presidential second terms are notably unproductive, most of all in their waning months. Since 2012 there has been nothing about the Obama presidency to justify the confidence that Democrats now exhibit.

Mr. Obama was elected in 2008 on the basis of his persona and his pledge to end political and ideological polarization. His apparent everyone-in-it-together idealism was exactly what the country wanted and needed. On taking office, however, the president adopted a my-way-or-the-highway style of governance. He pursued his stimulus and health-care proposals on a congressional-Democrats-only basis. He rejected proposals of his own bipartisan Simpson-Bowles commission, which would have provided long-term deficit reduction and stabilized rapidly growing entitlement programs. He opted instead to demonize Republicans for their supposed hostility to Social Security, Medicare and Medicaid.

No serious attempt—for instance, by offering tort reform or allowing the sale of health-insurance products across state lines—was made to enlist GOP congressional support for the health bill. It passed, but the constituents of moderate Democrats punished them: 63 lost their seats in 2010 and Republicans took control of the House.