On the last day of Barack Obama’s first year as president, the voters of Massachusetts, one of the few states more reliably Democratic than Washington, sent Republican Scott Brown to the U.S. Senate.

Kaboom.

What went wrong? The same thing that went wrong for the Democrats last November in Virginia and New Jersey. In those two gubernatorial elections, independent voters who had voted for Barack Obama voted 2-1 for the Republicans. In Massachusetts, where independents outnumber Republicans and Democrats combined, they swung almost 3-1 to Brown.

Why are the independents leaving? The president suggested that Brown won for the same reason he had a year earlier: the electorate remained angry about what had gone wrong in the previous eight years.

Really? The voters of Massachusetts sent a Republican to the U.S. Senate because they were still mad about George Bush?

Let me suggest an alternative explanation. In Massachusetts, Brown explicitly promised to oppose the centerpiece of the president’s domestic agenda: the National Health Care bill. It was far and away the biggest issue in the campaign. Brown even autographed posters with the number 41, pledging to be the vote necessary to prevent Obamacare from becoming law.

And voters responded, turning out in unexpectedly large numbers to give Brown a five-point victory. Independent voters seem to like the president personally, but they don’t like what he is doing or where he is headed.

The health care bill became a symbol of everything gone wrong in Washington, D.C. Rather than being written by the administration, the bill was outsourced (as was the massively expensive stimulus bill) to Congress. Taxes would go up. Spending would go up. Health care costs would continue to rise. To get the necessary votes, shady, expensive deals were cut right out in the open with Senators from Louisiana and Nebraska. Health care taxes would be exempt for union members only. Promises of transparency evaporated as late night, closed door meetings replaced open hearings. Even C-Span was stiff-armed.

Is this the “post-partisanship” voters were promised? Is this the “new tone” people were expecting to see? Those questions have already been answered by the voters of Virginia, New Jersey, and most emphatically, Massachusetts.

This has happened before. In 1992, with the Republicans divided, Bill Clinton, a young Southern governor campaigning as a unifying moderate, went to Washington with big majorities in Congress. He soon dropped his promise for a middle class tax cut and instead raised taxes while trying to enact a national health care bill. The result two years later was the first Republican House majority in nearly 40 years. But Clinton quickly did another about face. The liberal who supported midnight basketball in 1993 suddenly supported curfews and welfare reform three years later. By governing as the moderate he ran as in ’92, he kept his job in ’96.

That is what Obama should do if he wants to keep his job. Since he is more ideologically liberal than Clinton, he probably doesn’t want to do that. But the consequences for remaining stubborn will mean more people like Brown heading to Washington, D.C.

Come to think of it, that’s not a bad idea.