VICTORY MARCH: Eliot Spitzer, of New York, was one of six Dems to take back governorships from the GOP this fall.

Most political observers believe that the Democrats’ gains were mostly a one-time rejection of all things Republican, thanks to the worsening situation in Iraq and a host of ethics scandals in Congress. But there is good reason to think that this is just the beginning of a period of political ascendancy for the Democratic Party. A number of factors, long in development — from demographic trends to a favorable 2008 Senate reshuffling, and even a new-found, hard-won political competence in the Democratic Party itself — are lined up favorably, offering strong grounds for optimism among liberals.

Nobody’s counting any chickens before they hatch. But it’s worth noting that Americans aren’t showing any post–Election Day buyers’ remorse. On the contrary, they overwhelmingly approve of the Democrats’ impending takeover of Congress, and prefer a Democratic to a Republican presidential victor in 2008 by huge margins.

Here are four signs that 2006 will, in retrospect, mark the start of a new, blue era in American politics.

1) Congressional-numbers game
Although both houses of Congress just flipped to Democratic control, it was not by huge margins. But despite the thin leads, neither house is likely to flip back any time soon.

If anything, the Democrats’ slim 51-49 edge in the Senate figures to expand significantly in 2008, when the Democrats will have to defend just 12 of the seats they now hold, while 21 Republican seats will be in play. Some neutral observers are already predicting a four-seat gain for the Democrats in ’08 — and at least one Democratic pundit comes in at nine.

Observers are aiming high for Senate Democrats because most of their dozen open seats in 2008 are considered safe bets for the blue column. They include those currently held by John Kerry (MA), Richard Durbin (IL), Carl Levin (MI), Max Baucus (MT), Jack Reed (RI), Joe Biden (DE), and John Rockefeller (WV).

The Republican list includes some safe-looking seats too, but also quite a few tenuous ones.

Even some apparently safe GOP seats could look very different if Barack Obama is on the ’08 national ticket as the Democratic nominee for either president or vice-president. That could spur historic black turnout, potentially putting Senate seats in play in Mississippi, South Carolina, Virginia, North Carolina, and Georgia. The potential effect of Hillary Clinton on women’s turnout, or of Bill Richardson on Hispanics’, might also be felt, though presumably to a lesser extent.

In yet another good sign for Senate Dems, the Republicans will likely be plunged in infighting. In the lead-up to the 2006 midterm elections, the hard right, led by the ornery Club for Growth, challenged incumbent Republicans from the right. And it was perfectly willing to lose seats altogether on the altar of principle, as happened to Lincoln Chafee in Rhode Island. In 2008, the same could happen to Lindsay Graham, of South Carolina, among others.

You can understand why, despite the current narrow margin, Republicans fear they “may not have another realistic shot at getting the majority back until 2012,” as Chuck Todd recently wrote in the National Journal.

In the lower chamber, the Dems are also slated to keep their gains, and could also increase them. Political observers point out that the House of Representatives changes party control roughly as often as the Red Sox win the World Series. That’s largely because of the almost sure-bet re-election of incumbents. Blame it on whatever you want: district gerrymandering, campaign-finance law, name recognition, or the basic tendency of most voters to not change their minds dramatically in two years. The truism hasn’t changed. Even in last month’s dramatic shift, more than 94 percent of congressional incumbents running for re-election won — right in line with historical averages, as political analyst Charlie Cook has observed, although down from the 98-plus rates of the past five elections.

Barring the kind of radical national rejection just experienced by their counterparts, Democrats are unlikely to lose their House majority anytime soon unless a large number of Democrats in moderate districts resign, creating open battles.

In fact, exactly the opposite is likely, say observers like Mark Gersh, Washington director of the progressive National Committee for an Effective Congress [NCEC]. Republican congressmen, many of whom have never served in the minority, are about to find out just how little fun it is without the perks and privileges of power, he says. Don’t be surprised to see Republicans head for more lucrative offers in the private sector.

Meanwhile, fundraising and candidate recruiting is always harder for the minority party, and easier for the majority. “The DCCC’s [Democratic Congressional Campaign Committee] recruiting in ’06 was impressive, and I think ’08 will be even better,” Gersh says.