For every action, there is an equal and opposite reaction. That's Isaac Newton's third law of motion. It applies to politics just as much as it does to physics.

A case in point is the "You lie!" outburst by Rep. Joe Wilson, R-S.C., during President Obama's speech to a joint session of Congress on September 9. Action: Wilson's apparently spontaneous gesture of contempt. Reaction: Outraged Democrats rally to the cause of health care reform.

That is exactly what the president needs to happen. In his speech, Obama carefully tried to carve out a middle way between two objectives: building a consensus on health care reform ("I will continue to seek common ground in the weeks ahead") and standing up to his opponents ("If you misrepresent what's in the plan, we will call you out").

After meeting with Obama, moderate Democratic senators started to fall in line.

He seemed to get nowhere with Republicans. Their resolve strengthened over the summer because of conservative activists, who laid out a path of defiance. Sen. Bob Corker, R-Tenn., told The New York Times, "The point of the speech was to unify the president's Democratic base, not to advance policy."

If Obama can indeed unify his party, he wins. Democrats have solid majorities in both chambers. The name of the game in the House is 218 votes. There are 256 House Democrats.

Last week, the House Democratic whip count showed 44 moderate Democrats on record as opposed to the current House health care bill: 256 minus 44 equals 212 votes. The whip count also showed 57 liberal Democrats who have gone on record as saying they will vote against a health care bill that does not include a strong public option: 256 minus 57 equals 199 votes.

After Wilson's attack brought the conservative outrage from this summer's town hall meetings into the House chamber, Democrats started to pull together. Speaker Nancy Pelosi, D-Calif., had said before the speech, "In order to pass a bill in the House, it must have a public option." The day after the president spoke, Pelosi said, "This is about a goal. It's not about provisions." As long as a bill meets the goals of "affordability and accessibility and quality," the speaker said, "we will go forward with that bill."

After meeting with Obama, moderate Democratic senators started to fall in line. Sen. Ben Nelson, D-Neb., for example, said, "The method of getting everybody covered ... is secondary to the fact that you get it done, and that there is more than one way to do it."

Meanwhile, Democratic activists used Wilson's outburst to rally their party's rank and file. The Democratic Congressional Campaign Committee sent a message to backers: "Calling the president of the United States a liar in front of the nation is a new low even for House Republicans." Americans United for Change charged in a Web video, "It's official. The Party of No has become the Party of No Shame."

Democrats may be able to resolve their differences over reform legislation through the magic of "triggers." A public option would be held in reserve, triggered only if insurance exchanges failed to meet targets for expanding health coverage and reducing costs. That approach could satisfy liberals that the public option is still alive. Similarly, the legislation could include automatic spending cuts that would get made if the cost of health care reform started to drive up the deficit. That trigger could satisfy moderates that cost controls are serious.

In reality, triggers are politically dangerous, and they rarely get pulled. But they give political cover to members of Congress who can claim that the provisions they want will go into effect -- if needed.

We saw an elegant example of Newton's law in the days immediately after Obama's speech. Action: South Carolina Democrat Rob Miller, who challenged Wilson in 2008 and plans to challenge him again in 2010, quickly raised more than $1 million in campaign contributions. Equal and opposite reaction: The next day, Wilson's campaign reported that he, too, had raised more than $1 million.

Why is all of this good news for Democrats? Because there are a lot more of them in Congress. If they rally to the cause of health care reform and set aside, or paper over, their differences, the legislation will pass.

This article appeared in the Saturday, September 19, 2009 edition of National Journal.

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