President Donald Trump raised questions Wednesday night about a decades-old U.S. prohibition on testing its nuclear weapons by detonating them, a prospect which experts say is dangerous to populations and would open a door for adversaries to test and sharpen their most powerful weapons.

Former US President Donald Trump has claimed that Pakistan, along with Russia, China, and North Korea, is secretly conducting nuclear tests.

But that claim has been rejected by many nuclear experts and Mr. Trump’s own nominee to lead the U.S. Strategic Command, which is responsible for America’s ground-based, undersea and bomber-launched n...