Following the December school shooting at Newton, Connecticut, that left 20 children dead, Democrats and advocacy groups vowed to pass new gun laws in 2013.

The gun issue had long been considered political poison for Democrats, but for the first time gun control groups had the money to compete with the National Rifle Association. Billionaire New York City Mayor Mike Bloomberg pledged $12 million to gun control efforts. Americans for Responsible Solutions, the group of former Rep. Gabby Giffords, raised $11 million in four months.

2013 was the year gun control groups went on the offense—but the results were decidedly mixed.

1. Senate fails to pass gun control legislation

After negotiating for months, Democrats and moderate Republicans produced an amendment in April that would have expanded background checks for firearm purchases and strengthened laws against illegal gun trafficking.

But the bill fell four votes shy of the 60 needed to proceed. Four Democrats voted against the measure.

"This amendment would have criminalized certain private transfers of firearms between honest citizens, requiring lifelong friends, neighbors and some family members to get federal government permission to exercise a fundamental right or face prosecution," the NRA said in a statement.

"As we have noted previously, expanding background checks, at gun shows or elsewhere, will not reduce violent crime or keep our kids safe in their schools."

Senate Majority Leader Harry Reid (R., Nev.) shelved the bill. However, Reid has said he will reintroduce it when he has the votes to pass it.

Gun control advocates said their defeat would lead to a public backlash that would ultimately turn the tide against the NRA.

The backlash has yet to emerge.

2. President Obama: ‘A pretty shameful day in Washington’

Following the defeat of new gun laws in Congress, a visibly angry President Barack Obama, flanked by families from Newtown, chastised senators who voted against the bill.

"Families that know unspeakable grief summoned the courage to petition their elected leaders not just to honor the memory of their children but to protect the lives of all of our children," Obama said. "A few minutes ago a minority in the United States Senate decided it wasn't worth it."

The NRA did not shrink from the attack.

"[Obama’s] attacking the NRA, he's attacking our members, he's attacking citizens and senators of the United States, threatening them and all the rest," NRA President David Keene said in a radio interview. "I think that's really not a seemly way for the President of the United States to respond to a legislative defeat."

Meanwhile, gun control organizations poured their newfound wealth into a campaign against vulnerable senators who voted against the gun legislation, intent on making examples of them in the 2014 elections.

"We’ll get through this day, take down the bill, and get senators prepared for the fact that they are going to be dealing with this issue everyday for the foreseeable future until they resolve it in the way the public wants," Mayors Against Illegal Guns director Mark Glaze told BuzzFeed.

3. Colorado recalls two senators for gun control votes

On the state level, gun control advocates enacted sweeping new firearms restrictions in New York, California, and Maryland. However, similar legislation in Colorado ignited a recall effort against two prominent state senators.

What started as a grassroots campaign ballooned into a national proxy fight between pro and anti-gun lobbies. Gun control supporters, backed by Bloomberg, dropped more than $2 million into the race.

Despite the influx of outside money, Colorado voters ousted the two senators in the state’s first ever recall election. Although the new gun control laws are still on the books, the recalls sent a message to politicians that gun owners were still a force to be reckoned with.

"One thing is clear from the Morse defeat: Mike Bloomberg is political poison," NRA spokesman Andrew Arulanandam said in a statement to the Huffington Post.

4. McAuliffe wins in Virginia

Democratic gubernatorial candidate Terry McAuliffe beat Republican Ken Cuccinelli in November to become Virginia’s next governor, despite an "F" rating from the NRA.

Gun control supporters pointed to the victory as proof that the NRA was no longer invincible.

"If you think about this, Virginia is the home state of the NRA. That’s where their headquarters are," Bloomberg told CNN’s Jake Tapper. "If I had said to you twenty years ago that that a Democrat that is ‘F’ rated by the NRA …could win governor, you would have laughed me out of the room."

However, hot-button social issues, not guns, dominated the race. Polling showed voters were moved more by attacks on Cuccinelli’s stances on abortion and homosexuality than his gun record.

Nevertheless, McAuliffe’s win gives gun-control supporters a bully pulpit in an increasingly purple state.

5. As momentum fades, gun control groups vow to press on

With 2014 approaching, gun control advocates will likely look back on 2013 as the year that could have been. Nevertheless, gun control groups say they aren’t giving up the fight.

"It took six years, seven votes, three presidential administrations to pass the Brady law," the Brady Campaign’s Brian Malte told the Washington Post. "And we're not going away; we'll be here until we finish the job. We don't want it to be that long, but we'll do whatever it takes. We're going to see it through."

Any attempt at reviving the Senate legislation next year is going to be a heavier lift than last time. Public support for new gun laws has dipped back to pre-Newtown levels.

According to a recent NBC News/Wall Street Journal poll, 52 percent of Americans say they favor stricter firearm laws, while 38 percent think gun laws should remain the same. That number is down since February, when 61 percent of those polled favored new gun laws.

Meanwhile, an analysis of gun laws passed in the year since the Newtown shooting found that two-thirds of those laws loosened gun restrictions.