PALM CITY, Fla. On a trip here to Florida last week, President Obama joined former Gov. Jeb Bush at a Miami high school and stressed their common interest in education reform. That night, he made a cordial reference to Bush brother and son of Republican presidents at a Democratic fundraiser. When his comments were greeted with catcalls from the partisan audience, the president protested: "No, no, no, no, now." Then he added: "I know this is not a name you often hear at Florida Democratic fundraisers."

True. But Obama's comment was part of a deliberate strategy he has been following since the "shellacking" the Democrats absorbed last November. As he begins to organize his re-election campaign and road-test possible themes, the president is portraying himself as a bridge-builder, a consensus-maker, someone who is willing to find "common ground" with Republicans like Bush, even if it means catcalls and worse from his liberal supporters.

To understand this strategy, just look at the results of the 2008 election. A lot of attention has been focused on self-described "independents," and they are certainly important. Twenty-nine percent chose that label, and they favored Obama by 52 percent to 44 percent. But a more important target is "moderates," a group that includes many independents but also centrist, pragmatic members of both parties. This group was considerably larger than independents in 2008 comprising 44 percent of the electorate and they voted more heavily for Obama, 60 percent to 39 percent.

Obama's appeal to these centrists ran through everything he did and said in Florida. A delegation of teachers gathered outside the Miami high school, protesting the president's embrace of Bush and if you were a cynic (and we're not), you might even suspect that Team Obama bused in the critics to emphasize the moderate message.

At the fundraiser, the president returned to the same theme, praising Republican presidents from Abraham Lincoln to Dwight Eisenhower for investing in infrastructure improvements like railroads and highways. And then he declared: "The biggest contest we face is not between Democrats and Republicans. It's between the United States and our workers and our businesses and our economy and our competitors around the world."

This is clever and conscious. The president is portraying himself as the leader of the whole country, not just a party or a faction, a country engaged in a global battle for economic survival. And how do you object to that? There's not a big lobby in Washington that favors "losing the future."

But there's a paradox here. At the very moment that Team Obama is taking dead aim at moderate voters, Congress has fewer moderate members than ever. In fact, moderates are easily the least-represented group in American politics.

It has been a cliche for years, and an accurate one, to lament the "polarization" on Capitol Hill, but a new study by the National Journal shows exactly how serious the partisan divide has become. In fact, America is approaching a European model, with ideological parties that don't overlap in the middle and exert iron discipline over their members.

In the Congress that ended in December, the most conservative Democratic senator (Ben Nelson of Nebraska) had a more liberal voting record than the most progressive Republicans (George Voinovich of Ohio and Susan Collins and Olympia Snowe of Maine). Thirty years ago, when the National Journal started keeping these records, 58 senators occupied the middle ground between the polar extremes. Last year, there were none. As Trent Lott, the former Republican leader of the Senate, told the Journal: "Over the years, there is no question that the middle in the Senate has shrunk considerably."

If anything, the House has seen an even more dramatic shift toward ideological purity. In 1982, 334 House members posted ratings somewhere between the most liberal Republican and most conservative Democrat. By last year, the number had shriveled to seven, and today all but one of them Republican Walter Jones of North Carolina has left Congress.

There are many reasons for this pattern, but one of the most important is the rise of vocal advocates and pressure groups centered in cable TV, talk radio and the blogosphere that demand ideological purity and threaten reprisal against anyone who dares to stray from party orthodoxy.

In this world of shrill shouters, moderates have virtually no voice. But Obama knows they still hold the key to his re-election. And he intends to speak to them and for them.