On April 15, 2009: the day federal tax returns are due: a motley crew of protesters gathered in cities around the country. The demonstrators railed against big government, taxation, deficit spending, illegal immigration, the stimulus plan and other issues. Over the past 10 months, angry, sign-waving crowds have mobbed the streets of many American cities, denouncing progressive measures such as health care reform. Over time, the disparate groups of activists coalesced into a loose confederation of conservative populist groups known as the Tea Party Movement.

At first, mainstream politicians had no idea how to deal with the Tea Party movement. Progressive figures ridiculed the movement. After activists mailed teabags to their elected representatives to protest taxes, John Stewart mockingly called the group’s members teabaggers (ironically, mail screeners remove any teabags sent to representative’s offices for security reasons).

House Speaker Nancy Pelosi questioned the movement’s grassroots credentials, referring to Tea Party participants as inauthentic “Astroturf” activists planted by special interest groups. The movement also scared moderate Republicans, who feared that their party would be steered towards the extreme right.

So which is it? Are the teabaggers authentic grassroots activists? Do they present a strong challenge to the Democratic majority, or will they push Republicans to the extreme right, alienating moderate voters in the process?

Nancy Pelosi’s Astroturf allegations are not unfounded. The Tea Party Patriots: the organization behind many, if not most tea party rallies: have strong ties to Freedomworks, a conservative non-profit group. Freedomworks’ chairman is Dick Armey, a former Republican House Majority Leader and current corporate lobbyist.

More recently, a for-profit corporation organized a national Tea Party convention held on Feb. 5-7  in Nashville, Tenn. The conference’s keynote speaker, former Alaska governor Sarah Palin, received an appearance fee rumored to be more than $100,000. Exorbitant speaking fees at a for-profit convention led critics to question the movement’s grassroots status.

However, such quibbles can’t hide that the Tea Party movement tapped into a legitimate well of conservative discontent. Right or wrong, most of the Tea Party participants are not corporate plants but upset citizens, concerned that neither party will respond to their needs.

Indeed, the movement presents a real threat to moderate Republicans, as the movement has already shaken the Republican party. In August, a Democrat won a Congressional seat in New York that had been held by Republicans for 20 years after a Tea Party-endorsed candidate siphoned votes from the mainstream Republican nominee. In Arizona, Senator John McCain will face a far-right challenger in November’s general election. A Tea Party candidate will face Senate Majority Leader Harry Reid in Nevada, where the movement has qualified as a political party.

Some Democrats argue that the Tea Party movement will benefit progressives as Republicans move to the extreme right in response to Tea Party challengers, alienating moderate voters in the process. However, history shows that whenever the Republicans move further to the right (as they did during Newt Gingrich’s Republican Revolution), Democrats tend to follow.

President Obama cannot afford to let his party move further to the right. The Democrats’ broad political coalition, the so-called big tent, is already straining its foundations. Democratic leaders have tried so hard to placate moderate and conservative Democrats that they have enacted few meaningful policy changes despite strong majorities in both houses and control of the presidency. The party’s progressive base is already uneasy, and shifting further right would be disastrous.

The Democratic Party’s leadership should not try to court Republicans alienated by the Tea Party movement. Instead, they should focus on producing real policy change. As shown by the Republican majority’s collapse since 2000, political coalitions are never permanent. Policy change: like health care or climate change legislation: can last for decades.