In an emotional and, at times, tear-filled address, President Obama on Tuesday vowed to do something about the plague of gun violence and flexed his muscle via executive powers in an effort to slow the flood of firearms sales and help keep weapons out of the hands of potential gunmen.

Introduced by the heartbroken father of a Connecticut first grader who was killed three years ago by a gunman with an assault rifle at Sandy Hook Elementary School, Obama publicly directed federal agencies to expand background-checks on gun buyers and tighten enforcement of existing gun laws.

Obama told the gathering that the nation “has to feel a sense of urgency” on gun policy reform and stridently criticized previous efforts at reform and hamstrung by a GOP-controlled Congress. The president wiped away tears as he talked about the children who died during the mass shooting at Sandy Hook Elementary School.

“People are dying and the constant excuses for inaction no longer do, no longer suffice,” he said.

Under the new rules, anyone engaged in the business of selling guns has to obtain a federal seller’s license and do background-checks on the buyers.

“It doesn’t matter where you conduct your business — from a store, at gun shows or over the internet,” White House adviser Valerie Jarrett said on Monday. “If you’re in the business of selling firearms, you must get a license and conduct background checks.”

Obama’s initiative also calls for hiring hundreds of examiners to help the FBI do the increased background checks. And it requires weapons merchants to notify the ATF is their guns are lost or stolen.

Even before Obama announced his modest moves to keep guns out of the hands of criminals and the mentally ill, Republican presidential candidates vowed to undo his executive actions should they win the White House.

But for Obama, whose efforts on gun control became more forceful after Sandy Hook massacre, the moves were a long time coming.

“That was the worst day of my presidency, and it’s not something that I want to see repeated,” Obama said two weeks after Adam Lanza slaughtered 20 first graders and six staffers at the Sandy Hook school in Newtown, Conn.

After other mass shootings in Colorado, Arizona, Texas and South Carolina, Obama repeated his call for beefing-up gun control and banning assault weapons — only to be rebuffed by Congress and the powerful National Rifle Association.

Then, after last year’s mass shooting at an Oregon college that left 10 dead, a visibly angry and frustrated Obama complained “we have become numb to this.”

The president pushed back against criticism that his administration has tried to curtail Second Amendment rights.

“I believe in the Second Amendment,” the president said and added that those killed by gun violence in houses of worship had constitutional rights as well.

House Speaker Paul Ryan, and other Republicans, question the president’s position.

“No matter what President Obama says, his word does not trump the Second Amendment. We will conduct vigilant oversight. His executive order will no doubt be challenged in the courts,” Ryan said in a statement. “Ultimately, everything the president has done can be overturned by a Republican president, which is another reason we must win in November.”

Obama made his announcement amid polls that show most Americans favor gun control and as Democrats in blue states like California, Delaware and Oregon have passed measures to expand background checks and bar concealed weapons from college campuses.

“The gun lobby may be holding Congress hostage right now, but they cannot hold America hostage,” Obama said.

The NRA is now being challenged by pro-gun control groups like Americans for Responsible Solutions, which is led by shooting survivor and former U.S. Rep. Gabrielle Giffords, and Everytown for Gun Safety, which was founded by former New York City mayor Michael Bloomberg.

And instead of shying away from the hot-button issue to avoid angering gun owners in swing states like Pennsylvania and Ohio, Democratic presidential candidate Hillary Clinton has made reducing gun violence a centerpiece of her campaign as has Vermont Sen. Bernie Sanders, who previously opposed some gun control measures.

Thank you, @POTUS, for taking a crucial step forward on gun violence. Our next president has to build on that progress—not rip it away. -H — Hillary Clinton (@HillaryClinton) January 5, 2016

Their GOP rivals remain adamantly opposed to increased gun control — and on the side of the NRA. “We don’t beat the bad guys by taking away our guns,” Texas Sen. Ted Cruz, one of the GOP presidential candidates, has said. “We beat the bad guys by using our guns.”

This article originally appeared on NBCNews.com.