The Obama administration unveiled a series of executive actions Monday aimed at reducing gun violence and hoping to make progress in one of the most frustrating policy areas of the president’s tenure.

The package, which Obama plans to announce Tuesday, includes 10 separate provisions, White House officials said. One key proposal would require more gun sellers – especially those who do business on the Internet and at gun shows – to be licensed and force them to do background checks on potential buyers.

Obama would devote more federal funds to treating mental illness – a move that could require congressional approval – and require that any firearms lost in transit between a manufacturer and seller be reported to federal authorities.

Republicans in Congress and on the campaign trail have blasted the idea, and some advocates have threatened to challenge it in court. While it is modest compared with any legislation that Congress could adopt, it will still affect everything from how the federal government might leverage its purchasing power to advance “safe gun” technology to what information federal and local law enforcement will share on individuals who are illegally trying to buy weapons.

The president, who went over the initiatives in the Oval Office on Monday with administration officials such as Attorney General Loretta Lynch and FBI Director James Comey, said inaction by Congress in the wake of several mass shootings and other gun-related violence justifies his decision.

“It is my strong belief that for us to get our complete arms around the problem, Congress must act,” Obama said in brief remarks to reporters after the meeting. In lieu of that, he added, the actions he will announce “are well within my legal authority in the executive branch but also are ones that the overwhelming majority of the American people, including gun owners, support and believe in.”

One of the main provisions is new federal guidance requiring some occasional gun sellers to get licenses from the Bureau of Alcohol, Tobacco, Firearms and Explosives and conduct background checks on potential buyers. With no single threshold for what triggers the licensing requirement, it will be based on a mix of business activities such as whether the seller processes credit cards, rents tables at gun shows and has formal business cards.

Other aspects of the president’s plan aim to bolster the FBI’s background checks system, including a push by the U.S. Digital Service to modernize its processing operations and a proposal to add 200 ATF agents and investigators to bolster enforcement.

Obama will instruct federal agencies, which collectively represent the nation’s largest firearms purchaser to “explore potential ways” to promote technology that would prevent the accidental firing or unauthorized use of a gun, according to White House officials.

Another measure will require federally licensed gun dealers to report any lost and stolen guns to the National Crime Information Center. Over the past five years, according to the White House, an average of 1,333 guns recovered in criminal investigations each year were traced back to sellers who claimed they were missing but did not report them to authorities.

“This is a broad set of actions that tackles a variety of the issues related gun violence,” said Arkadi Gerney, a senior fellow at the liberal think tank Center for American Progress, “and in combination it represents a comprehensive effort to strengthen the laws we already have on the books.”

House Speaker Paul Ryan, R-Wis., by contrast, issued a statement Monday even without knowing the plan’s exact details, saying “the president is at minimum subverting the legislative branch, and potentially overturning its will. … This is a dangerous level of executive overreach, and the country will not stand for it.”

Though the number of mass shootings in the United States has risen in recent years, overall gun violence is at lower levels than in previous decades. Obama, however, emphasized that gun deaths in the United States remain higher than in other developed countries in almost every category, including suicides.

“We have to be very clear this is not going to solve every violent crime in this country, is not going to prevent every mass shooting, is not going to keep guns out of the hands of every criminal,” he said. “But it will potentially save lives in this country and spare families the pain and the extraordinary loss they’ve suffered.”

Obama’s determination to act in his final year in office comes after he pledged in the fall to make guns a political issue after a gunman killed 10 and wounded seven others at a community college in Roseburg, Oregon. The president has made public statements after at least 16 mass shootings during his presidency, including the killing of 14 people in San Bernardino, California, last month by a married couple, reportedly inspired by the Islamic State militant group.

His administration failed to persuade lawmakers to approve tighter legislative controls on gun sales in 2013, in the wake of the December 2012 killings of 20 elementary school students in Newtown, Connecticut. After that, the president issued a series of 23 executive actions to tighten controls and increase safety preparations. He added two more in subsequent years.

But the White House was moved to act again after the shootings at Umpqua Community College in Oregon. Administration lawyers have spent months reviewing various proposals to ensure that redefining what it means to be “engaged in the business” of selling firearms can withstand legal challenges.

“The law has long been fuzzy, and the transition of gun sales away from brick and mortar stores to gun shows and the Internet requires the administration to clarify the definition,” said Sen. Chris Murphy, D-Conn., who has urged Obama to act on his own. “By forcing more dealers at gun shows to run background checks, there will be less criminals that buy guns and less illegal guns sold on the streets of America.”

It is unclear how many sellers will now be required to obtain federal licenses, because the government does not currently track these informal sales. A 2001 survey of thousands of state and federal prison inmates by the Bureau of Justice Statistics found that more than two-thirds of those who had used guns in crimes had acquired them from sources other than licensed dealers and did not undergo background checks.

Dan Gross, president of the Brady Campaign to Prevent Gun Violence, said in an interview Monday that Obama’s initiative is “a historic step” that would subject thousands of gun sales each day to stricter scrutiny.

Obama is scheduled to talk about his new policies in the East Room on Tuesday, and will participate in a televised town hall at George Mason University two days later, televised on CNN.

“The president will only put forward executive actions in which he has confidence in their constitutionality,” White House Press Secretary Josh Earnest said Monday. Asked if the White House is concerned that Republicans or gun-rights advocates will challenge Obama’s actions, Earnest said: “I wouldn’t be surprised if they try, but the arguments we could mobilize in a court of law would be powerful and persuasive.”

One dilemma for the Obama administration would be that a legal fight could put the executive actions on hold as a court deliberates, potentially dragging out the process until Obama leaves office next January. The president’s executive actions to defer the deportations of millions of undocumented immigrants, announced in 2014, have been held up in a legal battle that could head to the Supreme Court this spring.

Obama’s plans already have resonated in the presidential campaign, where Republicans and Democrats have staked out very different positions on the question of how to address gun violence.

Even before the unveiling of the package, nearly a half-dozen Republican presidential candidates went on the attack. Every candidate who has spoken about it has vowed to reverse the executive order if elected president, underscoring the fragility of any initiative that lacks congressional approval.

Speaking at a Christian bookstore Monday in Boone, Iowa, Sen. Ted Cruz, R-Texas, called the idea “illegal and unconstitutional,” a theme echoed by several of his colleagues in recent days.

On Sunday, Sen. Marco Rubio, R-Fla., told an audience in Raymond, New Hampshire, that Obama “has waged war on the Constitution.”

“You can pass all the gun laws in the world that you want,” he said. “It will not stop the criminals.”

Democratic presidential candidate Hillary Clinton applauded Obama on Sunday for “taking a hard look” at the issue.

“I know that a Republican president would delight in the very first day, reversing executive orders that President Obama has made, including this one that we expect him to make,” she told a crowd in Derry, New Hampshire.