The announcement by Alabama Rep. Parker Griffith that he is switching to the Republican Party is just the latest warning sign that the Democratic Party — my lifelong political home — has a critical decision to make: Either we plot a more moderate, centrist course or risk electoral disaster not just in the upcoming midterms but in many elections to come.

Griffith's decision makes him the fifth centrist Democrat to either switch parties or announce plans to retire rather than stand for re-election in 2010. These announcements are a sharp reversal from the progress the Democratic Party made starting in 2006 and continuing in 2008, when it re-established itself as the nation's majority party for the first time in more than a decade. That success happened for one major reason: Democrats made inroads in geographies and constituencies that had trended Republican since the 1960s. In these two elections, a majority of independents and a sizable number of moderate Republicans joined the traditional Democratic base to sweep Democrats to commanding majorities in Congress and to bring Barack Obama to the White House.

These independents and Republicans supported Democrats based on a message indicating that the party would be a true Big Tent — that we would welcome a diversity of views even on tough issues such as abortion, gun rights and the role of government in the economy.

This call was answered not just by voters but by a surge of smart, talented candidates who came forward to run and win under the Democratic banner in districts dominated by Republicans for a generation. These centrists swelled the party's ranks in Congress and contributed to Obama's victories in states such as Indiana, North Carolina, Virginia, Colorado and other Republican bastions.

But now they face a grim political fate. On the one hand, centrist Democrats are being vilified by left-wing bloggers, pundits and partisan news outlets for not being sufficiently liberal, "true" Democrats. On the other, Republicans are pounding them for their association with a party that seems to be advancing an agenda far to the left of most voters.

The political dangers of this situation could not be clearer.

Witness the losses in New Jersey and Virginia in this year's off-year elections. In those gubernatorial contests, the margin of victory was provided to Republicans by independents — many of whom had voted for Obama. Just one year later, they had crossed back to the Republicans by 2-to-1 ratios.

Witness the drumbeat of ominous poll results. Obama's approval rating has fallen below 49 percent overall and is even lower — 41 percent — among independents. On the question of which party is best suited to manage the economy, there has been a 30-point swing toward Republicans since November 2008, according to Ipsos. Gallup's generic congressional ballot shows Republicans leading Democrats. There is not a hint of silver lining in these numbers. They are the quantitative expression of the swing bloc of American politics slipping away.

Despite this raft of bad news, Democrats are not doomed to return to the wilderness. The question is whether the party is prepared to listen carefully to what the American public is saying. Voters are not re-embracing conservative ideology, nor are they falling back in love with the Republican brand. If anything, the Democrats' salvation may lie in that Republicans seem even more hell-bent on allowing their radical wing to drag the party away from the center.

All that is required for the Democratic Party to recover its political footing is to acknowledge that the agenda of the party's most liberal supporters has not won the support of a majority of Americans — and, based on that recognition, to steer a more moderate course on the key issues of the day, from health care to the economy to the environment to Afghanistan.

For liberals to accept that inescapable reality is not to concede permanent defeat. Rather, let them take it as a sign that they must continue the hard work of slowly and steadily persuading their fellow citizens to embrace their perspective. In the meantime, liberals — and, indeed, all of us — should have the humility to recognize that there is no monopoly on good ideas, as well as the long-term perspective to know that intraparty warfare will only relegate the Demo-crats to minority status, which would be disastrous for the very constituents they seek to represent.

The party's moment of choosing is drawing close. While it may be too late to avoid some losses in 2010, it is not too late to avoid the kind of rout that redraws the political map. The leaders of the Democratic Party need to move back toward the center — and in doing so, set the stage for the many years' worth of leadership necessary to produce the sort of pragmatic change the American people actually want.