WASHINGTON -- Here's a question rarely raised before Donald Trump ran for the White House: If the president ordered a pre-emptive nuclear strike, could anyone stop him?

The answer is no.

Not the Congress. Not his secretary of defence. And by design, not the military officers who would be duty-bound to execute the order.

The president has what some call unchecked authority to order a nuclear strike against any country he wants.

But even leaders of the Republican Party are now questioning whether he has too much power over weapons that threaten civilization.

The Senate holds a hearing Tuesday to examine the protocol for ordering and carrying out a presidential nuclear order, and whether it should be changed.