If Barack Obama loses his bid for reelection, the main reason can be traced to one period of time and one choice.

In late 2009, the Democratic-controlled House and Senate had both passed health-reform legislation and were proceeding with reconciliation talks. But in January 2010, Democrats lost Ted Kennedy’s Massachusetts Senate seat — as well as their filibuster-proof Senate majority — in a protest against Obamacare. It was a remarkable revolt, in the bluest of states.

“If there isn’t any recognition that we got the message and we are trying to recalibrate and do things differently,” Rep. Anthony Weiner (D-N.Y.) said at the time, “we are not only going to risk looking ignorant but arrogant.” Rep. Eric Cantor (R-Va.) predicted that if the Obama team pushed through a final health bill along party lines, Democrats would “lose their majority in Congress in November.” The concerns of some on the Obama team preceded the Massachusetts debacle. White House Chief of Staff Rahm Emanuel had argued for a more incremental approach to health reform. “I begged him not to do this,” he later recalled.

The president went ahead, saying, “I feel lucky.” In March 2010, Obamacare was passed without a serious recalibration or a single Republican vote.

This choice unleashed a cascade of effects. Obama placed a highly ideological debate on the size and role of government at the center of U.S. politics. He contributed to extreme polarization in Congress and the public. He exhausted his political capital on an issue that had little to do with the immediate economic crisis the country was facing. He invited the backlash midterm election of 2010 — including the loss of 63 Democratic House seats — which effectively ended the creative period of his presidency.

Obama achieved all of this with a quick and dirty legislative shove that further discredited the political process. The final bill was passed through a maneuver — the reconciliation process — that embittered opponents and assured that a future GOP majority would engage in retribution. The final votes were secured through federal promises to states that smacked of bribery. “I think that the manner in which the health-care reform was put in front of the Congress, the way that the issue was dealt with by the White House, cost Obama a lot of credibility as a leader,” says retiring Sen. Jim Webb (D-Va.)

In claiming victory following passage of the bill, Obama said, “This is what change looks like.” Which was precisely the problem. Change came in the form of a law that a plurality of Americans opposed, at a time when other issues were more urgent, by methods that disgraced its advocates. “I think we paid a terrible price for health care,” retiring Rep. Barney Frank (D-Mass.) recently concluded.

The evidence is found in the current campaign. Obama’s signature legislative accomplishment is a relatively minor theme of his reelection effort. It is hard to crow about a law that presidential scholar George Edwards calls “perhaps the least popular major domestic policy passed in the last century.” So Obama’s closing argument on health care is mainly a divisive, unqualified defense of abortion rights.

Obamacare matters in the current election not only because its future is at stake but for what its passage tells us about Obama as a leader. He is stubborn, which can be an admirable trait when applied to the public interest. But on health-care reform, Obama combined stubbornness with ideological predictability and partisan ruthlessness — imposing a very conventional liberalism in the Chicago way.

Obama tends to overestimate his own negotiating skills with Congress, which are poor (and were also displayed in his failed attempt to achieve a grand budget compromise in 2011). When the ideological stakes are highest, Obama jettisons bipartisanship with little thought or regret. He was perfectly willing to reorganize one-sixth of the economy on a party-line vote. He has employed tactics that ensure future partisan bitterness. His persuasive powers on the issue of health care turned out to be limited. The more he spoke, the less public support he found. But he proved incapable of creative ideological readjustment.

Obama’s largest achievement turned out to be a self-indictment. He has not shown the leadership skills or the inclination to create consensus around large issues. The problem is that large issues — avoiding the fiscal cliff, reforming the tax code, making entitlement commitments more sustainable — are coming. Either Obama will have to become an entirely different type of leader — or America needs a new one.