U.S. military COULD refuse Trump's order to launch a nuclear attack

Retired Air Force Gen. Robert Kehler told the Senate Foreign Relations Committee during a hearing today that the president's power to awaken the United States' nuclear arsenal is not totally unchecked.

If an 'illegal order' to strike North Korea or some other country is handed down, the military is 'obligated' to refuse it, said Kehler, a former commander of the Pentagon's nuclear weapons division.

'That would be a very difficult process, and a very difficult conversation,' he added. 

The assessment was part of a pained discussion Tuesday on Capitol Hill about Trump, in the context of his provocative warnings to North Korean dictator Kim Jong-un.