WASHINGTON — The Pentagon released a new nuclear arms policy Friday that calls for the introduction of two new types of weapons, effectively ending Obama-era efforts to reduce the size and scope of the US arsenal and minimize the role of nuclear weapons in defense planning.
Secretary of Defense Jim Mattis said in an introductory note to the new policy — the first update since 2010 — that the changes reflect a need to ‘‘look reality in the eye’’ and ‘‘see the world as it is, not as we wish it to be.’’
The Obama administration’s policy hinged on what the former president called a moral obligation for the United States to lead by example in ridding the world of nuclear weapons. But officials in the Trump administration and the US military argue that Obama’s approach proved overly idealistic, particularly as Russia reemerged as a foe, and failed to persuade US nuclear adversaries to follow suit.
‘‘Over the course of the last several years, Russia and China have been building new types and kinds of nuclear weapons, both delivery systems and actual warheads,’’ Air Force General Paul Selva, vice chairman of the Joint Chiefs of Staff, told journalists earlier this week.
‘‘We have not, which means the capability of Russian and Chinese nuclear arsenals is actually getting better against ours,’’ Selva said.
The new nuclear weapons policy follows on President Trump’s promise before taking office to expand and strengthen US nuclear capabilities. Trump also vowed during his State of the Union address Tuesday to build a nuclear arsenal ‘‘so strong and powerful that it will deter any acts of aggression.’’
The threats have changed dramatically since the last time the Pentagon updated its nuclear weapons policy, with Russia re-emerging as a geopolitical foe and both Moscow and Beijing investing in their nuclear arsenals.
North Korea, meanwhile, has edged closer to possessing a missile capable of striking the US mainland with a nuclear warhead, bringing the prospect of nuclear war back to the forefront of the American psyche for the first time since the Cold War.
Trump’s perceived volatility has raised more concerns among Americans about the president’s exclusive authority to order a nuclear attack.
The policy unveiled Friday envisions the introduction of so-called ‘‘low-yield nukes’’ on submarine-launched ballistic missiles.
Russia has a large arsenal of small nuclear weapons that the United States mostly lacks. The Pentagon worries that Moscow could seize part or all of a US ally state and then detonate a small nuclear weapon to prevent American troops from coming to the rescue.
Washington would be forced to choose between launching a much-larger-scale nuclear attack on Russia or responding with less serious conventional arms that would make Washington look weak. The Pentagon says it wants a proportionate weapon to match.
A draft of the new policy prompted an outcry from disarmament advocates, who assailed the Trump administration for pursuing what they described as unnecessary new nuclear weapons that could start an arms race.
Critics also accused the Department of Defense of lowering the threshold for what might provoke a US nuclear strike by mentioning cyber attacks in the list of nonnuclear strategic threats.
‘Russia and China have been building new types and kinds of nuclear weapons. . . . We have not.’
With just a week before the Olympic Games begin on the Korean peninsula, Trump on Friday sought to increase pressure on Pyongyang over its nuclear program by consulting with allies and highlighting the human rights abuses suffered by defectors from North Korea.
Also Friday, Trump visited the National Targeting Center of the US Customs and Border Protection department in Sterling, Va. At a meeting with top homeland security officials, the president said their jobs would be ‘‘100 percent easier’’ with the right laws.
Trump said the immigration proposal he has sent to Congress is needed to protect the borders. The White House has proposed creating a path to citizenship for up to 1.8 million young people living in the county illegally. In exchange, it wants billions of dollars for a border wall and dramatic cuts to legal immigration.