President Obama's State of the Union speech Tuesday night happened at a time of heightened awareness about guns in America, but it was barely mentioned during his address.

The topic of gun control has been incessantly frustrating for Obama. Gun advocates still fear he wants to take their guns away, even though he says he doesn't. Every time he mentions gun control, gun sales surge.

Responding to recent mass shootings, including the one last month in San Bernardino that claimed 14 lives, Obama has unveiled executive actions on gun control.

To drive home the importance of this act, Obama left a seat vacant to represent the victims of gun violence during his State of the Union address.

But he only mentioned gun control once, as part of a list of actions he plans to take in his last year as president. "And I'll keep pushing for progress on the work that still needs doing. Fixing a broken immigration system. Protecting our kids from gun violence," Obama said.

What does Obama want to do on guns?

Obama's gun control plan is primarily a clarification of how he intends to enforce existing law.

He wants to add more than 400 agents to the ATF and FBI to beef up their ability to conduct background checks.

And he wants to scrutinize those who are selling guns without a federal license. Are they really just collectors who are trying to unload a couple of guns? Or are they clandestine gun dealers operating under the radar?

What do Obama's critics and supporters say?

The NRA and other gun advocates see his executive action as draconian overreach. Supporters of gun control see the action as a necessary measure to try and curb gun-related violence. Either way, it lacks teeth compared to Obama's gun control bill, which failed to get through the Republican-dominated Senate in April 2013.

The most important element of the bill was to close the gunshow loophole by expanding federal background checks to all gun sales, including those between non-dealers.

Related: 2015 was record year for background checks

All sales conducted by gun dealers, who are licensed by the federal government, are subjected to federal background checks. Eighteen states impose additional background checks on all handguns, even between non-dealers, and 10 of those state impose background checks on all guns, including rifles and shotguns.

But in the majority of states, people can sell guns to each other without background checks, so long as they're not federally licensed dealers. If this loophole seems murky or vague, that's why Obama wants to clarify it. He wants to bolster the ranks of federal agents who keep tabs on these deals, and he wants to know how many guns these unlicensed dealers are selling.

Obama gets criticized and mocked by gun advocates, who view every piece of gun control legislation as an incremental violation of the Second Amendment, even though Obama has tried many times to reassure them it's not.

What's happening on gun control outside Washington?

But Obama is not the sole force in gun control. Where the president has fallen short, state lawmakers have succeeded in requiring universal background checks, restricting assault rifles and mandating limits on magazine capacity.

Since Newtown, six states have mandated background checks for all gun sales, including Connecticut and also Colorado, where a gunman armed with an AR-15 with a 100-round drum shot 70 people at a movie theater in 2012, killing 12 of them.

Related: How background checks work

Connecticut and Colorado have also placed limits on magazine capacity, which was a key element to Obama's failed gun bill.

"I would disagree that Obama failed," said Shannon Watts, founder of Moms Demand Action, an arm of the Bloomberg-supported gun control group Everytown for Gun Safety. "I think Congress failed. [The gun bill] would have been a national solution to a national crisis."

She said that Obama's executive action is "not the silver bullet," but it's valuable nonetheless.

"'He was not able to close the loophole, but he was able to narrow it," she said.