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 U.S. arsenal and minimize the role of nuclear weapons in defense planning.

The previous administration’s policy hinged on what President Barack Obama 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 U.S. military argue that Obama’s approach proved overly idealistic, particularly as Russia reemerged as a foe, and that it failed to persuade U.S. nuclear adversaries to follow suit.

The policy unveiled Friday envisions the introduction of “low-yield nukes” on submarine-launched ballistic missiles.

Russia possesses a large arsenal of small nuclear weapons, something the United States mostly lacks. The Pentagon worries that Moscow could seize part or all of a U.S. 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.

“One of the most disturbing and significant changes to U.S. policy outlined in the NPR is the tighter integration of U.S. nuclear and conventional forces, including training and exercising with these integrated forces, so U.S. forces can operate—as the NPR states—in the face of nuclear threats and employment. This is the text-book definition of nuclear war-fighting. This new policy deliberately blurs the line between nuclear and conventional forces and eliminates a clear firewall.

“The decision to deploy another type of low-yield weapon—this one on submarines—is consistent with the new emphasis on nuclear war-fighting. Existing U.S. B61 bombs and air-launched cruise missiles already have low-yield options.

“The administration’s new policy also shoots a big hole in the Nuclear Non-Proliferation Treaty, which is key to U.S. security. It simply rejects the U.S. obligation to take steps toward nuclear disarmament. Since the end of the Cold War, the United States has made progress—albeit slow progress—in reducing the number, types and role of its nuclear weapons. The new policy reverses that progress. The NPR is a giant slap in the face of the non-nuclear weapon states, who are already fed up with the slow progress of the United States and Russia.

The new policy described in the NPR broadens the scenarios under which the United States would use nuclear weapons first, thus lowering the threshold for first use. The document explicitly lists a wide array of non-nuclear attacks that could constitute grounds for a US nuclear response. These “include, but are not limited to, attacks on the U.S. allied or partner civilian population or infrastructure, and attacks on U.S. or allied nuclear forces, their command and control, or warning and attack assessment capabilities.”