If you’re thinking that last week’s tragedy in Newtown, Conn., makes it likely that Congress will soon pass stricter federal gun laws, remember this: People thought the same thing in 2011, after a gunman shot into a Tucson crowd, killing six and injuring others, including Gabrielle Giffords, one of the House of Representatives’ own members.

Public support for gun control tends to swell after a mass shooting. But then, just as quickly, it tends to ebb, and opponents are happy to wait the process out.

Tougher gun control laws face an array of obstacles. The National Rifle Association and its allies are still a powerful lobby. The fervor for more regulation is almost exclusively among Democrats; the Republican majority in the House is still solidly opposed. And there’s that inevitable erosion of public attention once the heartbreaking images of funerals fade.

But it’s possible that the latest round of calls for regulation could end differently, and not only because the murder of 20 young children is so horrifying.

This time, the debate will take place in a very different political landscape, and that’s probably more important, in Congress’ calculations, than the emotional impact of the Newtown murders.

Consider the differences between today and last summer, when there was a brief clamor for stricter gun laws after a gunman killed 12 people in an Aurora, Colo., theater. Back then, it wasn’t clear whether President Obama could win a second term, and it seemed likely that the GOP would retake the Senate. Congressional Republicans saw no reason to compromise, and Obama didn’t have political capital to waste.

When the president was forced to talk about the issue in an October debate, he began this way: “I believe in the 2nd Amendment. We’ve got a long tradition of hunting and sportsmen and people who want to make sure they can protect themselves.”

But on Wednesday, when he announced that he was directing Vice President Joe Biden to bring him proposals for quick action against gun violence, Obama’s tone was different. For the first time, he made gun control a formal part of his second-term agenda. “I will use all the powers of this office to help advance efforts aimed at preventing more tragedies like this,” he said. “We won’t prevent them all, but that can’t be an excuse not to try.”

On Election Day, when Obama won handily, it wasn’t votes from gun owners that put him over the top. Instead, the president won by mobilizing a Democratic majority among groups that are overwhelmingly in favor of gun control: women, suburban voters and Latinos.

The most important number in this week’s polls on gun control isn’t the spike in overall support for more regulations — 54 percent in a Washington Post/ABC News poll this week, the highest in five years; that was to be expected. More important, as Greg Sargent pointed out in the Post, is the demographic breakdown of that support. Democrats, college-educated voters, women and minorities favor stricter gun regulations by significant majorities. Opposition to gun control is concentrated among white men, especially white men who didn’t go to college.

Those demographics have several political consequences.

First, the opponents of gun control are mostly voters Obama and his party have already lost to the Republicans, so by being cautious on the issue, Democrats aren’t gaining much. (Democrats representing districts in the South and the Mountain West are likely to still tread carefully.)