First, the numbers. As of this writing, there has been a 29-seat Democratic gain in the U.S. House. Of those, 18 Democratic freshmen, were endorsed and actively aided by at least one of two centrist groups: the Blue Dog Democrats and the New Democrat Coalition. A half-dozen were supported by both coalitions, including newly elected Rep. Heath Shuler in North Carolina.

These two groups, though both centrist, are far from identical. The Blue Dogs were formed first, just after the 1994 Republican victories. Founded by Democrats primarily in the South, Midwest, and inner West, the group argued that reflexive liberalism on social issues and an appearance of fiscal imprudence had damaged the party’s national prospects, as well as the prospects of Democratic candidates in swing districts. The name was invented before the advent of the media convention to label Republicans red and Democrats blue. It is a riff on the old saying that some Democrats were so loyal they would vote for a yellow dog as long as it had a “D” beside its name. The founding members of the Blue Dog Democrats complained that liberalism had choked their kind blue. Before Election Day, there were 37 Blue Dogs. In January, there will be at least 44.

The New Democrat Coalition came along a few years later, in 1997. Its name was a conscious nod to the brand personified by the original new Democrat, President Bill Clinton. The 2006 election added at least 15 members to the coalition, which will number at least 63. While the Blue Dogs have emphasized moderation on social-issues and the importance of balanced budgets, the New Democrats describe their agenda as “pro-growth” and often focus on foreign policy, innovation, and technology issues. Not to exaggerate the differences between the two groups, whose membership does overlap, but they do have distinct identities and priorities. Consider their takes on four important issues: trade, taxes, immigration, and abortion.

Most New Democrats have embraced free trade, a policy that was associated with Clinton, after all. That doesn’t mean they all voted for every trade agreement; indeed, only 15 Democrats voted for the Central American Free Trade Agreement in 2005. But this issue still distinguishes the coalition ideologically from the Blue Dogs, many of whom vociferously oppose free trade and view it as a major factor damaging the manufacturing economies of the small towns and rural communities they represent. Joe Donnelly, an incoming Blue Dog, won Indiana’s 2^nd District in part by stressing his opposition to CAFTA and past deals with Chile and Singapore. In the state’s 8^th District, Democrat and former sheriff Brad Ellsworth soundly defeated Republican John Hostettler, complaining during the campaign that “for far too long, Washington has allowed American jobs to be shipped overseas.”

On taxes, New Democrats often stress growth-enhancing tax policies, including lower rates on dividends and capital gains, while Blue Dogs often oppose tax cuts without advocating spending cuts to fight the federal budget deficit. Democratic leaders who want to raise taxes in the future, or allow the Bush tax cuts to expire, will not find much support from either group. Ellsworth signed the Americans for Tax Reform no-tax-hike pledge. Tim Mahoney, the investment banker who won Mark Foley’s seat in Florida and was endorsed by both the New Democrats and the Blue Dogs, is on record favoring significant reduction or elimination of estate taxes.

As for immigration, President Bush’s initiative combining border enforcement with a guest-worker program will find more support among the New Democrats than the Blue Dogs. Nearly half of the 64 Democratic votes for a House bill to build a 700-mile fence on the Mexican border came from Blue Dogs, and some of the group’s incoming members leaned towards the restrictionist camp during their campaigns. Some of the candidates endorsed by the New Democrats, on the other hand, represent areas with high-tech companies and offered some support for Bush-style “comprehensive” reform. In a notable race, Democrat Gabrielle Giffords, whose opponent was incumbent Randy Graf, a nationally prominent champion of the enforcement-only position, won Arizona’s 8^th District while talking tough about immigration. When it came to policy, however, she aligned herself with John McCain’s legislative approach to the issue.

Six of the new centrist Democrats — Shuler, Donnelly, Ellsworth, Chris Carney and Jason Altmire of Pennsylvania, and Ohio’s Charles Wilson — proclaimed themselves to be pro-life. Other centrists, particularly among the Blue Dogs, while they may not go that far, could well vote for future measures on issues such as partial-birth abortion and parental consent. Most New Democrats cannot be considered reliable votes for anti-abortion legislation. The National Right to Life Committee has estimated a net loss in the 2006 cycle of 10 to 15 pro-life votes in the House and four in the Senate.

Some conservatives and Republicans — Newt Gingrich, for instance — are urging President Bush to take a page from Ronald Reagan’s first-term playbook, assembling congressional coalitions of Republicans and moderate-to-conservative Democrats to pass legislation on tax policy, budget reform, and other issues. It sounds like a great idea, but finding the 50 or 60 Democratic votes necessary for a Center-Right majority isn’t simply a matter of rounding up the centrists. Many of these centrists will oppose Bush on some combination of fiscal, trade, and social issues. And the Republican caucus is not so cohesive as to allow for such simplified legislative arithmetic, as last month’s vote on trade with Vietnam demonstrated. A good number of New Democrats and Blue Dogs may well vote to block liberal legislation initiated on Capitol Hill — on gun control, for example — but that doesn’t mean they will easily join the president on his agenda. After all, many of them were elected by running at least as strongly against Bush as against their Republican opponents.