Last night was a great one for the Democratic party. A president re-elected and a Senate majority expanded, even if the House remains in Republican hands.

But beyond the headlines, consider for a moment the underlying dynamics of this win: Democrats have now won the popular vote in five of the last six presidential elections. Among 18-29-year-old voters, the Democratic advantage actually slipped from four years ago, but Obama still won them by 23% – a huge majority among the next generation of voters. Obama increased the party's edge with Hispanic voters, winning an extraordinary 71% of their votes. These numbers are replicated obviously among African Americans, but also Asian Americans where the party has a similar near-monopoly. Even as Obama lost white voters by 20 points (which is 8 points worse than 2008), he still won the electoral college handily.

Last night, we saw the emergence of a new Democratic governing majority – one that was hinted at in 2008 – with the potential to serve as the foundation of presidential politics for many years to come. Quite simply, Democrats have once again become the nation's presidential party.

So what does this mean for actual governing? Here, we need to consider the other big winner from last night: liberals.

The left wing of the Democratic party has long had something of a fractured relationship with its national leadership – they have been the vanguard of Democratic political victories, but have often received only half a loaf on policy issues. But if last night is any indication, national Democrats and, in particular, President Obama will have to take the concerns of liberals far more seriously.

Consider the evidence: Obama's winning message was very much one of a traditional Democrat. He ran against tax cuts for the wealthy; was a strong defender of Medicare, Medicaid and the social safety net; and relied on the promise of real immigration reform to win such a large segment of the Hispanic population. He didn't back away at all from progressive stances on key social issues. And while healthcare reform and financial regulation were hardly the key messages of Obama's campaign, it's hard not to view last night as a validation of these policies.

Neither Obamacare nor Dodd-Frank will be repealed. While the country may not be completely sold on healthcare reform, people's misgivings were not enough to undermine Democrats at the polls. When you consider the policy agenda that Obama ran on, last night looks like a big win for the policy goals of liberals.

And look, too, at some of major ballot initiatives from last night. Going into election day, whenever the issue of gay marriage had been on the ballot in the US, it was batting a dreadful 0-32. This Tuesday night, it went 4-4, winning in a diversity of states – Maryland, Maine, Minnesota and Washington. Now, granted each of the states is blue, but what these wins indicate is that supporting equal rights for gays is no longer a political liability. The arc of civil rights for gay Americans is bending toward progress. In fact, it may only be a matter of time before support for gay marriage is as de rigueur in the Democratic party, as is being pro-choice. In addition, advocates of legalizing recreational use of marijuana won referendums in Colorado and Washington.

Finally, there is the actual make-up of the Democratic caucus in Congress. Barack Obama might have delivered a stirring speech about the need for Americans to come together and work toward shared goals, but if Democrats in Congress have anything to say about it, those goals will almost certainly have a leftward tilt.

First, there is the House. Not long ago, Democrats had to abide by the concerns of their more moderate southern and "blue-dog" brethren. Well, this is going to be less of an issue going forward because there aren't many of those centrists left. Many were wiped out in 2010, and while Congressman John Barrow inexplicably won his contested congressional seat in Georgia, the Democratic party, by and large, no longer has a southern wing. Actually, let me correct that: Democrats no longer have a southern white wing.

By one measure, the Democrats are now down to about a dozen blue-dog moderates. That creates a caucus in the House of Representatives that is more decisively liberal and non-southern than perhaps at any point in history.

What about the other end of Capitol Hill, in the US Senate? We are seeing a similar phenomenon there: moderates like Joe Lieberman and Ben Nelson, who consistently thwarted the Democratic agenda in Congress, are gone. So, too, are Jim Webb and Kent Conrad. They join a steady stream of moderate and conservative Democrats who have left Congress and are increasingly being replaced by a far more liberal group of senators.

Last night, it was the populist Elizabeth Warren in Massachusetts and the first openly gay member of the Senate, Tammy Baldwin, in Wisconsin. They will join fellow liberals like Sherrod Brown in Ohio, Amy Klobuchar in Minnesota and Debbie Stabenow in Michigan, all of whom easily won re-election.

This is the new face of Democrats in Congress: one that is more diverse – and also more left-leaning. This will have serious implications for President Obama's governing agenda. While it will still be nearly impossible for him to pass progressive legislation, with Republicans controlling the House of Representatives, in places where compromise is necessary – like the Bush tax cuts and sequestration – Obama will now have to take into account the concerns of liberals.

It always seemed far-fetched to me that the president would agree to benefit cuts for major social insurance programs like Medicare or social security, but after last night, it seems even more unlikely. Democrats in Congress won't abide it.

Beyond the president's legislative goals – and the "constraints" imposed by liberals in Congress – Obama will have to curry favor with his increasingly left-leaning governing coalition. You've already seen this on an issue like gay marriage. But on immigration, in which Obama pursued a strong enforcement strategy during his first two years in office, he will need to get serious about pushing comprehensive immigration reform. If necessary, he will need to use executive power to liberalize rules for the country's millions of undocumented immigrants, a policy shift that already began during the last year of Obama's first administration. If Democrats want to consolidate the loyalty of Hispanic voters, this should be one of Obama's top priorities.

On issues like the environment and labor relations, Obama will be pushed to use his regulatory powers, as head of the executive branch, to take more progressive positions. Liberals who have demanded that the president more aggressively pack the federal bench with the next generation of left-leaning jurists will be demanding more action on this front – and perhaps a push from the White House for reform in the Senate to make it easier to have these new judges confirmed.

One of the chief complaints against Obama is that he relied too much on Congress to push his policies and failed to use the powers of the presidency as a tool for reform. Pressure to do just that will increase – and it will come not only from the left, but also from Obama's own desire to get something done in the face of strong House Republican opposition to his policies.

Finally, on foreign policy, liberals held their powder on the use of drones, the war in Afghanistan and other civil liberties-related issues. Will they continue to hold their fire? Some in Congress probably will, but there will be even greater pressure from the activist community for the president to show more transparency in these areas. And, with the president freed from the shackles of seeking re-election, they are likely to see progress on this front.

For four years, Obama hinted that he was, at heart, a progressive realist. Beginning in January, there's a reasonable possibility that guy might end up putting his stamp on foreign policy going forward.

In the final analysis, 6 November was a big win for Democrats: a confirmation that they are increasingly becoming the nation's dominant political party, with significant demographic and policy advantages over Republicans. For liberals, the victory is even sweeter, because not only is their party getting more progressive, but so, too, it seems, is the nation.