President Obama went to the East Room of the White House on Tuesday prepared to announce modest new restrictions on gun sales across the country, but the moment quickly turned into one of the most emotional public episodes of his presidency.

The 37-minute speech became part eulogy, part admission of political failure and part constitutional lecture on the Second Amendment.

Eventually, the president cried.

Flanked by more than a dozen men and women, many of whom he had consoled privately shortly after they lost loved ones to gun violence, Obama summoned the memory of nearly two dozen children killed three years ago in their Connecticut school. He decided on the new curbs unilaterally, he said, because guns have cut short too many American lives.

“Every time I think about those kids, it gets me mad,” he said, wiping a tear from his right eye. “And, by the way, it happens on the streets of Chicago every day.” This time he flicked away a tear from his left cheek.

President Obama formally announced a set of executive orders on gun control on Jan.5. Here is what you need to know about how the regulations tighten gun sales and expand background checks. (Claritza Jimenez/The Washington Post)

The president was introduced by Mark Barden, whose son Daniel, 7, was slain in the 2012 shooting at Sandy Hook Elementary School. People in the audience held up photos of their dead loved ones as Obama began his remarks.

[After Sandy Hook shooting, mourning parents enter the lonely quiet]

In a speech that veered from somber to outraged, and was punctuated by moments of humor, the president said he was trying to bring the country together on a divisive issue at a time when he does not have to worry about the political fallout.

“I’m not on the ballot again. I’m not looking to score some points,” he said, adding that he does not believe that the new standards violate the Constitution: “We understand there are some constraints on our freedom in order to protect innocent people.”

A key provision of the new initiative would require more gun sellers — especially those who do business on the Internet and at gun shows — to be licensed and therefore to conduct background checks on potential buyers. Another measure would mandate that firearms lost in transit between a manufacturer and a seller be reported to federal authorities. And more than 230 additional examiners and staff members would be hired to help the FBI process background checks 24 hours a day.

The plan came under immediate attack from Republicans. Senate Majority Leader Mitch McConnell (Ky.) called it “President Obama’s Political Gun Control Announcement.” A slew of GOP presidential candidates derided Obama’s actions and leveraged them in fundraising appeals. Former Florida governor Jeb Bush said that Obama “has proved again why he will go down as one of the most liberal and divisive presidents in the history of our nation.” The campaign of Sen. Ted Cruz (Tex.), which had already made images showing the president in body armor and under a tactical helmet, told potential donors in multiple appeals over the past few months, “Obama wants your guns.”

Obama said it will take congressional action to fully address the problem, but his actions Tuesday clearly fulfilled a pledge he made to “politicize” gun violence ahead of the 2016 elections.

While formally announcing executive orders on gun control on Jan. 5, President Obama said that, "Second Amendment rights are important, but so are other rights" such as freedom of religion and freedom of assembly. (Associated Press)

“Our unalienable right to life, and liberty, and the pursuit of happiness — those rights were stripped from college students in Blacksburg and Santa Barbara, and from high schoolers at Columbine, and from first-graders in Newtown,” he said, pausing. “First-graders.”

Obama spoke in a room packed with Democratic politicians, including House Minority Leader Nancy Pelosi (Calif.), and with gun-control advocates, including shooting victims and family members of those killed by gunfire.

Former representative Gabrielle Giffords (D-Ariz.), shot at point-blank range during a mass shooting in 2011, entered with a cane, accompanied by her husband, Mark Kelly. Giffords shook hands with Attorney General Loretta E. Lynch and received a standing ovation as she took her seat in the front row, next to Obama senior adviser Valerie Jarrett. The two held hands, with Giffords regularly squeezing Jarrett’s, as Obama spoke.

Actress Amy Schumer, a cousin of Sen. Charles E. Schumer (D-N.Y.) and a gun-control advocate, also sat in the front row, as did the two young daughters of the late Rev. Clementa Pinckney, who was killed in a mass shooting at Emanuel AME Church in Charleston, S.C., last year.

Jarrett said the arrayed grief overwhelmed Obama, whose reputation for stoicism and aloofness is well-earned.

“He looked around the room and saw people who he had met over the last seven years on the worst days of their lives,” Jarrett said later. Those losses, she said, coupled with inaction in Congress, make it “just hard to fathom. That frustration spilled out today — that’s what everybody saw.”

With the background-check measure, the administration is clarifying what it means to be “engaged in the business” of selling firearms. This does not constitute new regulation, which would have been subject to public comment and congressional review, but its application depends entirely on how aggressively federal authorities press the matter.

Scott Hamblin, a firearms dealer with Guns Midwest, said in an email that there “are licensed dealers and individuals and nothing in between, never has been. . . . It appears to me that the White House figured out today that they just wanted to enforce the current law and that explains the addition of new ATF agents.”

The initiative comes after gun transactions hit a record high in 2015, with background checks for purchases and permits rising 10 percent over the previous year, to 23.1 million.

[Firearms sales spike amid concerns over terrorism, Obama’s gun-control policies]

Gun-safety activists said the measures could help interrupt trafficking of some illegal firearms and could embolden other politicians to enact more sweeping restrictions in the future.

“This is significant in the signal it sends, culturally,” said Shannon Watts, founder of Moms Demand Action for Gun Sense in America.

In the Washington suburbs, Montgomery County Police Chief J. Thomas Manger praised Obama’s proposals as “a great step in the right direction.” Manger, whose police force covers a Maryland county of 1 million people, also serves as president of the Major Cities Chiefs Association. “There are too many guns that are sold out of a trunk of a car to a person who would not be able to pass a background check, and that’s how many guns get into the wrong hands,” Manger said. “The fact is we need universal background checks. And, again, this is a no-brainer.”

Even with the reduced political consequences of not running for office again, Obama conceded the difficulty ahead. “Yes, it will be hard, and it won’t happen overnight,” he said. “It won’t happen during this Congress. It won’t happen during my presidency.”

Some lawmakers have raised the idea of blocking the plan by halting funding for the FBI or the Bureau of Alcohol, Tobacco, Firearms and Explosives. But Sen. Rand Paul (R-Ky.), who opposes the president’s executive actions, said that would be difficult, since lawmakers agreed on a budget deal last month that will keep the government running through September 2016.

“Once you give up the ability to let spending expire, you need 60 votes to defund something — and now, there aren’t 60 votes to defund anything,” said Paul, who is also a presidential candidate. “If we had courage and guts, which most of the time we do have, we could vote on a new spending bill which blocks funding for new gun-control orders. That was why so many of us thought the omnibus was a bad idea.”

The National Rifle Association and other gun rights advocates have pledged to fight the measures, even as they described the administration’s push as minimal in scope.

“The American people do not need more emotional, condescending lectures that are completely devoid of facts,” said Chris W. Cox, executive director of the NRA’s Institute for Legislative Action. He added that the group’s members are concerned about public safety, “but the fact is that President Obama’s proposals would not have prevented any of the horrific events he mentioned.”

Obama said the point of his executive actions is “not to debate the last mass shooting but to do something to try to prevent the next one.”

As Jarrett walked back to the Oval Office with the president after the speech, she carried handwritten notes from Mark Barden and his wife, Jackie, thanking Obama and Vice President Biden for their efforts in trying to prevent a repeat of the rampage that cost them their son.

She slipped them into the president’s inbox, so he could read them later.

Dan Morse and David Weigel contributed to this report.