A new investigative report on Monday sheds light on the United States’ modernization of its nuclear arsenal and the details are troubling: weapons that are smaller, more accurate, and potentially more likely to be used—and a president who, critics say, has turned his back on hope for a global weapons ban.

Under President Obama, the Energy Department and the Pentagon have been modernizing existing weapons to produce “a smaller, more reliable arsenal,” write New York Times reporters William Broad and David Sanger, which allows Obama to claim allegiance to his 2010 pledge to end the development of new U.S. nuclear warheads or capabilities.

One such model, the B61 Model 12, “is the first of five new warhead types planned as part of an atomic revitalization estimated to cost up to $1 trillion over three decades,” the Times reports. “As a family, the weapons and their delivery systems move toward the small, the stealthy and the precise.”

Last year the bomb was flight-tested by the U.S. government in the Nevada desert. At the time, Russia’s Deputy Defense Minister Anatoly Antonov slammed the tests as “irresponsible” and “openly provocative.”

Internally, the updated arms have set off concerns that the once “unthinkable” deployment of a nuclear warhead may now enter the realm of the possible.

Though he backed the upgrades, Gen. James E. Cartwright, one of the president’s most influential nuclear strategists and former vice chairman of the Joint Chiefs of Staff, acknowledged to the reporters that “what going smaller does…is to make the weapon more thinkable.”

In a subsequent interview, Cartwright expressed concern that the overall modernization plan, and the new precision of the weapons, could alter how military officials assess the risk of using nuclear weapons. “Does it make them more usable?” Cartwright asked. “It could be.”

SCROLL TO CONTINUE WITH CONTENT