The Democratic Party controls the House, the Senate, and the Whitehouse. Congress will most likely pass, and the President will sign, major legislation that will reform the healthcare system of the United States. It will go way beyond fixing the "problems" that exist under the current system. It will change almost a fifth of the nation's economy.
Current polls show that most Americans are opposed to this effort. But it will happen anyway.
So, why would our elected representatives do something that most of the nation opposes? Because they can. Because they think they can get away with it. This is the calculation that they've made.
The success of that calculus depends on opposition being too disorganized, or unfocused to win the next elections. Considering that the Greens would prefer more than what we'll get, the Republican Party is lost, Libertarians are generally unelectable, and the Tea Party is most a local movement, there is merit to that assessment.
But depending on the incompetence of your opponent is a poor strategy. Beware of underestimating your the American people. They might surprise you.