Now here's something you don't hear in every political era: "Many US Senators are concerned the president** is nuts." **so-called

David Corn at Mother Jones:

As [the Senate foreign relations committee] questioned three experts—retired Gen. C. Robert Kehler, a former commander of the US Strategic Command, Peter Feaver, a professor at Duke University, and Brian McKeon, a former acting undersecretary of policy at the Pentagon—the point was repeatedly made that Trump has the ultimate and sole authority to send nuclear weapons flying. This is especially true in the case of the United States facing an imminent threat, such as a foreign adversary launching (or preparing to launch) a nuclear strike against the United States. In these circumstances, the president would have minutes to decide whether to order a nuclear assault. There would be little time for the president to consult with anyone but a few advisers before reaching a decision. The nation and the rest of the world would be at his mercy.

Chris Murphy (D-CT) didn't sugarcoat it:

“We are concerned that the President of the United States is so unstable and is so volatile…that he might order a nuclear weapon strike that is so wildly out of step with US national security interests.”