Four years ago, the election of Barack Obama was so historic that many wondered if a new American era had begun. And then came the 2010 midterm elections. Although the president’s party usually loses seats in midterms — the loss in 2010 was especially bad, making people wonder if the 2008 election had been a fluke after all — a function of the financial meltdown that occurred in September of 2008. Any Democrat, it was argued, could have won in 2008.

If you were going by the economic models, Barack Obama should not have won re-election last night. Economic growth, no matter how you measure it, has simply been too slow. Previous presidents paid for this at the polls — but Obama did not. The fact that he could transcend an economy that has defeated others tells us something about the president’s own talents but it tells us a lot more about who we are and where we are going as a nation.

When voters gave the president four more years, questions about the 2008 election were answered once and for all. It wasn’t a fluke. In fact, it’s ushered in a new American era.

As the 2012 campaign approached, the grandiloquence about the Obama presidency faded into the humdrum business of government. The recession got better but unemployment dragged on, we killed Osama bin Laden only to realize that there were more terrorists out there waiting to kill our ambassadors, and the oceans continued to rise and wipe out the Jersey shore.

Nonetheless, when voters gave the president four more years, questions about the 2008 election were answered once and for all. It wasn’t a fluke. In fact, it’s ushered in a new American era. It is now probable that 2008 marked the beginning of what political scientists call a realignment. Realignments are marked by the coming of age of a new, unique, and very large generation. Because the oldest members of this generation came of age at the turn of the century, this new generation is called the millennials. Unlike its generational predecessors, this new generation is more diverse (40 percent are of African American, Latino or some other non-Caucasian descent); more tolerant (gay marriage isn’t even an issue for most of them); and more liberal and Democratic in their politics than previous generations.

But even more important, this new generation is large. After a long and gradual slide, American birth rates picked up in 1985 and rose quickly thereafter. The baby-boomers, a little slow to reproduce, finally did and the “echo boom,” long in coming, had arrived.

President Barack Obama waves as he walks on stage with first lady Michelle Obama and daughters Malia and Sasha at his election night party Wednesday, Nov. 7, 2012, in Chicago. (Carolyn Kaster/AP)

Morley Winograd, author (along with Mike Hais) of the best selling book “Millennial Makeover” was the first to describe this generation and what it would mean for politics. As he told me last night, “In 2012, 19 million more members of the millennial generation became eligible to vote and made up all of the 18-29 year olds surveyed in exit polls. As a result, millennials made up 19 percent of the electorate this year and once again voted overwhelmingly for Obama, 59 to 37 percent. As all of this generation turns 18 by 2020, it is clear that their attitudes and beliefs will determine not only who wins in national elections but which kind of policies the nation favors."

The coming of age of the millennials marks the sort of turning point in American politics that requires a long backward look to fully understand. But doing so shows us that there are generations that, molded by a common experience, transform politics for their lifetime.

In 1828 a new generation of rugged frontier men elected Andrew Jackson president and dominated politics for the next three decades. Thanks to Abraham Lincoln, Republicans dominated American politics from 1860 to 1932, when the great depression brought Franklin Roosevelt to power. After that, Democrats won 78 percent of the presidential elections until 1968. Then from 1968 until 2008, Republicans won 70 percent of the time.

After Tuesday night, we can expect a new era of Democratic dominance. In addition to the presidential election, the party easily retained control of the Senate; something they were not expected to do even a year ago. The same generational dynamic that helped the president, also helped Democrats like Missouri Senator Claire McCaskill. McCaskill, who was considered to be one of the most vulnerable Senate candidates, was supported by 68 percent of voters between the ages of 18 and 29 and by 55 percent of voters between the ages of 30 and 44. In Indiana, another state that was expected to elect a Republican Senator, the Democrat Joe Donnelly defeated Richard Mourdock by getting 48 percent of the votes of the 18 to 29 year olds and 53 percent of the 30 to 44 year olds. In both races the Republican candidates made statements about rape that were way out of the mainstream, perpetuating a “war on women” totally at odds with the sentiments of the new and upcoming generation of millennials.