Gen. Joe Dunford, nominated to become chairman of the Joint Chiefs of Staff, created some headlines in a Senate confirmation hearing by naming Russia as the No. 1 threat that the U.S. faces. “They present the greatest existential threat,” he told the Senate Armed Services Committee at his confirmation hearing. “If you look at their behavior, it’s nothing short of alarming.” He then cited China and North Korea as other top-tier threats, followed by Islamic State.

Some commentators have noted that his answer diverges slightly from that of James Clapper, director of national intelligence, who told Congress earlier this year that cyber-attacks were the No. 1 threat that we face. “Cyber threats to U.S. national and economic security are increasing in frequency, scale, sophistication and severity of impact; [and] the ranges of cyber threat actors, methods of attack, targeted systems and victims are also expanding,” Clapper testified before Congress. His words have gained additional resonance as the size of the computer breach at the Office of Personnel Management has become clearer.

So which is it: Russia or cyber? North Korea or China? ISIS or Al Qaeda? And don’t forget Iran and the potential of terrorists getting their hands on nuclear weapons. What’s our greatest threat?

For what it’s worth, I would cite terrorists with WMD as our top threat, but there is a strong case to be made for all of the others as well.

Debating that question is a nice parlor game, but it is divorced from the real world reality that as a superpower the U.S. has to be ready for all these threats — and more. Indeed, the greatest danger could emanate from a quarter that we can barely perceive as of yet, what Don Rumsfeld called “the unknown unknowns.”

In the face of so much risk (and today’s geopolitical environment is the most volatile in my lifetime), security comes from having armed forces ready at a moment’s notice to respond to a host of contingencies. But we are depriving ourselves of that capability through ill-advised across-the-board budget cuts that will reduce defense spending by roughly a trillion dollars over the course of this decade.

Those cuts are already beginning to bite, with the army announcing that it is laying off 40,000 troops to shrink to 450,000 active-duty personnel, its lowest level since 1940. Gen. Ray Odierno, the Army chief of staff, has just warned that his service can’t get any smaller and still meet its obligations, but it is likely to shrink to just 420,000 personnel unless sequestration is repealed. The Air Force, meanwhile, is down to 315,000 personnel, its lowest level since the service’s creation in 1947. And the Navy, which needs to have well over 300 ships to meet existing requirements, has only 273 ships deployable at the moment.

Little wonder that Dunford told the Senate Armed Services Committee: “What keeps me up at night is our ability to respond to the unexpected. On balance, our force can deal with the challenges that we have now. But there is very little residual capability.” And what little capacity we have is rapidly shrinking.

This should be — but isn’t — one of the top issues in the presidential campaign. Whatever one may think of how to deal with this foreign policy crisis or that one, one truth remains eternal: Every problem will become harder to manage if the U.S. does not have the military capacity to back up its diplomacy.