'For the first time in over 40 years, Congress has examined a US president's authority to launch a nuclear attack.
The Senate Foreign Relations Committee hearing was titled Authority to Order the Use of Nuclear Weapons.
Some senators expressed concern that the president might irresponsibly order a nuclear strike; others said he must have the authority to act without meddling from lawyers.
The last time Congress debated this issue was in March 1976.
In August, Mr Trump vowed to unleash "fire and fury like the world has never seen" on North Korea if it continued to expand its atomic weapons programme.
Last month, the Senate committee's Republican chairman, Senator Bob Corker, accused the president of setting the US "on a path to World War III".'
Read More: Senate committee questions Trump nuclear authority