The writer is addressing the question: Should a Democrat challenge President Obama in the 2012 primaries?

Patrick Buchanan in 1992, Edward Kennedy in 1980, even Ronald Reagan in 1976 - what do they all have in common?

Not only did they fail to be elected president - Reagan had to wait four more years - but by taking on an incumbent in their own party, they helped deliver the White House to the opposition.

Some progressives have indicated support for such a challenge in 2012. To them I ask: Do you really want Mitt Romney, Rick Perry or Herman Cain as the most powerful person in the world? I served under House Speaker Newt Gingrich, and I can assure you that the prospect of a President Gingrich is even more unsettling.

A primary challenge would be a lose-lose - it would be hugely unsuccessful but would leave President Barack Obama bruised and weakened for a tough general election campaign against the Republican nominee. Far from ushering in a progressive renewal, the result could be an extreme right-wing monopoly on control of the federal government.

Every day in the House, my fellow Democrats and I are fending off a radical tea party agenda. Just imagine if that agenda were being pushed by the White House with the support of a Republican Congress.

If my pro-primary friends truly want government of, by and for the 1 percent - if they want more anti-choice Supreme Court Justices, no improvements to health-care reform, attacks on labor unions, and cuts to Social Security and Medicare - then by all means they should abandon the president's campaign and embrace a primary opponent.

Some have suggested that Secretary of State Hillary Clinton should or would challenge the president, but she has clearly and categorically ruled it out. She is too smart and too committed to her outstanding work as the nation's top diplomat to contemplate such a reckless and counterproductive move.

All this is said by an unapologetically outspoken progressive who has disagreed more than I like to admit with the Obama administration. We will of course continue to push back on the president when we think he has lost his way, but we must also have his back when gets it right. We should urge him to be bold, reminding him who his base is, but not actively undermine him during a pivotal election year when the other choice on the ballot is unthinkable. We should not be blind followers, but nor should we be petty spoilers.

Whatever Democratic appetite there is for a primary fight - and I believe it is minimal - is based on a misunderstanding of what animates President Obama. The president is who he is - enormously intelligent and dynamic, and an extremely cautious and moderate politician. In 2008, many voters confused a historic candidacy and great personal charisma with their own agenda and hopes.

Also, with a Republican Congress obstructing every positive step for change, there is a limit to what the president can accomplish.

In 2009-2010, his partnership with Speaker Nancy Pelosi and a Democratic majority produced a jobs bill that rescued the nation from the economic abyss; the Affordable Care Act that expanded health coverage to 32 million more Americans; historic financial reform; and the Lily Ledbetter Fair Pay Act - quite a lot when you consider the debacle he inherited from the Bush administration.

Democrats have a reputation for snatching defeat from the jaws of victory, allowing ideological purity to get in the way of smart politics. With so much at stake, we cannot afford to do that in 2012.

Let's not make the perfect the enemy of the good. Let's put aside our disappointments and circle the wagons around the one viable presidential candidate who shares our values. Let's endorse President Obama for re-election and do everything we can to assure his victory next November.

Rep. Lynn Woolsey, D-Calif., is president of Americans for Democratic Action.