President Barack Obama unveiled an array of measures on Tuesday tightening control and enforcement of firearms in the U.S., using his presidential powers in the absence of legal changes he implored Congress to pass.

Obama accused the gun lobby of taking Congress hostage, but said "they cannot hold America hostage." He insisted it was possible to uphold the Second Amendment while doing something to tackle the frequency of mass shootings in the U.S. that he said had become "the new normal."

Obama wiped tears from his cheeks as he spoke emotionally about the victims of gun violence.

Obama on gun control: 'How did we get here?'37:16

"This is not a plot to take away everybody's guns," Obama said in a ceremony in the East Room. "You pass a background check, you purchase a firearm. The problem is some gun sellers have been operating under a different set of rules."

At the centrepiece of Obama's plan is a more sweeping definition of gun dealers that the administration hopes will expand the number of sales subject to background checks. Under current law, only federally licensed gun dealers must conduct background checks on buyers.

But at gun shows, websites and flea markets, sellers often skirt that requirement by declining to register as licensed dealers. So new federal guidance from the Obama administration clarified that it applies to anyone "in the business" of selling firearms.

The White House also put sellers on notice that the administration planned to strengthen enforcement — including deploying 230 new examiners the FBI will hire to process background checks.

NRA: 'Ripe for abuse'

The National Rifle Association said Obama's executive actions on gun control are "ripe for abuse" and lack seriousness.  

The largest U.S. gun group is accusing Obama of political exploitation for announcing the steps in the last year of his presidency. Chris Cox, who runs the NRA's lobbying arm, said the actions wouldn't have prevented any of the mass shootings that Obama mentioned.  

Cox said Obama is trying to distract from his lack of a strategy to prevent terrorist attacks in the U.S. He said Americans don't need any more "emotional, condescending lectures that are completely devoid of facts."

Support for Obama's gun control measures5:06

To lend a personal face to the issue, the White House assembled a cross-section of Americans whose lives were altered by the nation's most searing recent gun tragedies, including former Rep. Gabrielle Giffords and relatives of victims from Charleston, S.C., at Virginia Tech.

Mark Barden, whose son was shot to death at Sandy Hook Elementary School, introduced the president with a declaration that "we are better than this."

 Barden's group was particularly appreciative of Obama's focus on getting people more access to mental health care. Expanded mental health treatment was among the measures the president announced Tuesday.

Obama challenged those in Congress who blame mass shooting on mental health to "put their money where their mouth is."

Earlier, invoking the words of Martin Luther King Jr., Obama said, "We need to feel the fierce urgency of now."

Texas Sen. Ted Cruz said Obama's measures aren't worth the paper they're written on.

Clinton, Sanders praise

During a campaign stop in Onawa, Iowa, the Republican presidential candidate repeated his promise to repeal all of Obama's executive actions, including the latest ones on guns.

Pro-gun group reacts to Obama gun control announcement9:42

"When you live by the pen, you die by the pen," Cruz said. And he added that his own pen "has an eraser on it."

Democratic presidential contender Hillary Clinton tweeted her thanks to the president. She called his executive actions "a crucial step forward on gun violence."

And she added that the next president "has to build on that progress--not rip it away."

Clinton's Democratic opponent, Vermont Sen. Bernie Sanders, also praised the president's actions.

Sanders says he'd continue Obama's actions if elected president.

Sanders accused Republicans of placing the interests of the National Rifle Association ahead of children and innocent Americans.

With files from CBC News