The top general in charge of the American nuclear arsenal said he would like to see the primary arms-control treaty between the United States and Russia grow to encompass all nuclear weapons, instead of limiting a select few, as President Trump considers whether to renew the agreement.

Air Force Gen. John E. Hyten, commander of U.S. Strategic Command, said the New START treaty benefits the American military by capping Russia’s baseline strategic nuclear force and offering “unbelievably important” insight, through inspections, into what Russia is doing.

But Hyten warned that many of the nuclear systems Russia is introducing — including a thermonuclear torpedo and a hypersonic glide vehicle that President Vladimir Putin has touted in the past year — fall outside the restrictions of the treaty. So does Russia’s vast arsenal of small nuclear arms sometimes described as “battlefield” or “tactical” nuclear weapons.

“I am a big supporter of the New START agreement,” Hyten told the Senate Armed Services Committee on Tuesday. “I want, ideally, in my view, all nuclear weapons to be part of the next phase of New START and not just the identified weapons that are part of the New START treaty.”

The general’s comments come at an inflection point in nuclear arms control. Signed by President Barack Obama in 2010, New START expires in less than two years. If the Trump administration declines to renew it, the world will return to an era without any legally binding or verifiable limits on its two biggest nuclear powers for the first time since 1972.

Citing violations by Russia, the Trump administration formally announced early this month that it would pull out of the Intermediate-Range Nuclear Forces Treaty, or the INF Treaty, the other primary arms-control agreement remaining between Washington and Moscow.

Soon, Trump will have to decide whether to extend New START, let the treaty expire or attempt to replace it with some new pact that encompasses a broader range of nuclear weapons by engaging in new negotiations. One question facing the White House is whether efforts to broker a more expansive agreement would risk the dissolution of New START’s benefits as they stand.

“The president asks me about that every time I see him,” Hyten said Tuesday when asked whether the administration would renew New START. “It’s high on his mind.”

Russia has indicated an interest in prolonging the pact. Speaking to Fox News after meeting Trump in Helsinki last year, Putin said he stood ready to renew the treaty but added that the two countries must first agree on the specifics, “because we have some questions to our American partners.”

New START continued and modified limits on strategic nuclear arms that date back to the Cold War. The treaty restricts the number of deployed intercontinental ballistic missiles, submarines and heavy bombers to 700 at any one time. It limits the number of deployed warheads on those platforms to 1,550.

The pact includes a clause that allows the United States and Russia to renew it for up to five years automatically if the leaders of both countries agree. Because both the United States and Russia have already reduced their warhead numbers to the agreed-upon limits, an extension would simply keep those caps in place and continue the inspections.

On Tuesday, Hyten praised those inspections as “hugely beneficial to me.” He described how the treaty allows inspectors from the United States to land at a port of entry in Russia, declare where they want to go, and look at a nuclear site to verify that the right number and kind of weapons are there. Russia’s inspectors can do the same in the United States. 

“We have very good intelligence capabilities, but there is really nothing that can replace the eyes-on, hands-on ability to look at something,” Hyten said. “So we have to do that. But there are elements that they have that are not elements of the New START treaty that we don’t have insight into.”

Hyten said that with regard to getting Russia back into compliance with the INF Treaty and working on a follow-on agreement to New START, he is paying close attention to what the State Department is doing. “They are reaching out to the Russians, and the Russians aren’t answering favorably,” he said.

Russian Foreign Minister Sergei Lavrov, meanwhile, told Putin this month that the United States had failed to engage with Russia’s efforts to negotiate the renewal. 

“All they say is that a decision about the fate of the New START treaty has not been made,” Lavrov told Putin. “All in all, the situation is worrying.” 

Hyten warned that while he is confident he can defend the United States in any foreseeable situation for the next 10 years, he worries about the prospect of defending against Russia after that. 

“I get concerned, 10 years and beyond, that with torpedoes, with cruise missiles, with hypersonics, that they could go a completely other direction that we would have a difficulty,” Hyten said. “But I don’t have any problems standing here and saying I can defend this nation today, and I think the commander after me can, but I worry about the commander after the commander after the next.”

He said he supports New START, but if Russia continues to build capabilities outside the treaty and refuses to come to the table to discuss new strategic arms that appear, “that causes me to have concerns.”