Here’s how President Obama states the nuclear paradox:

The risk of a nuclear confrontation between nations has gone down, but the risk of a nuclear attack has gone up.

Here’s how I define it:

Hypothetical nuclear threats provoke more fear than real nuclear threats.

Nowhere is this paradox more evident than in Tel Aviv and Tehran.

Which city is currently in greater jeopardy of nuclear annihilation? Tehran.

Which city’s residents are repeatedly being told by their political leaders they should be afraid of nuclear annihilation? Tel Aviv’s.

So, to return to Obama’s assessment, when he says the risk of nuclear confrontation between nations has gone down, he’s saying something that’s both obvious and deceptive. What’s obvious is that the Cold War risk of a nuclear war between nuclear-armed states has diminished, but what he purposefully did not say is that the risk of any nuclear-armed state actually using its nuclear weapons has gone down.

The risk that Israel could use tactical nuclear weapons to destroy Iran’s nuclear facilities is real. I don’t believe that Israel is likely to do so because its current leadership — despite its willingness to engage in hyperbolic rhetoric — probably recognizes that the regional and global impact of the first use of nuclear weapons in warfare since 1945 would seal Israel’s fate as a pariah state.

Still, the risk that Israel might use nuclear weapons is indisputably greater than the risk of nuclear weapons being used by any organization or state that is not currently armed with such weapons.

The risk of nuclear terrorism should not be dismissed, but as Brian Michael Jenkins notes, it’s important to distinguish between nuclear terrorism and nuclear terror. In 2008 he wrote:

Will terrorists go nuclear? It is a question that worried public officials and frightened citizens have been asking for decades. It is no less of a worry today, as we ponder the seventh anniversary of 9/11.

Might Iran’s nuclear weapons ambitions lead eventually to arming Hizbollah or Hamas with nuclear weapons? Might a financially desperate North Korea sell the wherewithal for nuclear weapons to terrorist buyers? Might a political upheaval in always turbulent Pakistan put a nuclear weapon in the hands of extremists? Could there, ultimately, be a nuclear 9/11?

We have to take the long-shot possibility of nuclear terrorism seriously, but we must not allow ourselves to be terrorized by it.

Nuclear terrorism and nuclear terror reside in different domains. Nuclear terrorism is about a serious threat — the possibility that terrorists might somehow obtain and detonate a nuclear weapon — while nuclear terror is about the anticipation of that event. Nuclear terrorism is about terrorists’ capabilities, while nuclear terror is about imagination.

Fear is not free. Fear can pave the way for circumventing established procedures for the collection of intelligence, for attempts to operate outside the courts, and perhaps for torture. Distinguished scholars discuss the durability of the U.S. Constitution in the face of nuclear terrorism.

Frightened populations are intolerant. Frightened people worry incessantly about subversion from within. They worry about substandard zeal. Frightened people look for visible displays to confirm unity of belief–lapel pin patriotism.

Fear creates its own orthodoxy. It demands unquestioning obeisance to a determined order of apprehension.

During the Cold War an all-out nuclear exchange would have meant planetary suicide. Today, we face one tyrant in North Korea with a handful of nuclear weapons, an aspirant in Iran enthralled by first-use fantasies, and a terrorist organization with an effective propaganda machine-dangerous, vexing, but not the end of the world, not the end of the nation, not the end of a single city.

Undoubtedly, a terrorist nuclear explosion of any size would have a huge psychological impact on America. But whether it would lead to social anarchy would depend heavily on the attitudes of the nation’s citizens and the behavior and communications of its leadership.

We may not be able to prevent an act of nuclear terrorism. But we can avoid destroying our democracy as a consequence of nuclear terrorism.

Whether or not we as citizens yield to nuclear terror is our decision.

John Mueller from Ohio State University’s department of political science wrote last year:

The evidence of al-Qaeda’s desire to go atomic, and about its progress in accomplishing this exceedingly difficult task, is remarkably skimpy, if not completely negligible. The scariest stuff — a decade’s worth of loose nuke rumor — seems to have no substance whatever. For the most part, terrorists seem to be heeding the advice found in an al-Qaeda laptop seized in Pakistan: “Make use of that which is available … rather than waste valuable time becoming despondent over that which is not within your reach.”

As Mueller and Mark G. Stewart note in an article in the current edition of Foreign Affairs, if America’s counterterrorism policy was actually based on objective risk assessment, we’d understand that the risk al Qaeda poses to each American is about the same as the risk posed by kitchen appliances.

As a hazard to human life in the United States, or in virtually any country outside of a war zone, terrorism under present conditions presents a threat that is hardly existential. Applying widely accepted criteria established after much research by regulators and decision-makers, the risks from terrorism are low enough to be deemed acceptable. Overall, vastly more lives could have been saved if counterterrorism funds had instead been spent on combating hazards that present unacceptable risks.

This elemental observation is unlikely to change anything, however. The cumulative increased cost of counterterrorism for the United States alone since 9/11 — the federal, state, local, and private expenditures as well as the opportunity costs (but not the expenditures on the wars in Iraq or Afghanistan) — is approaching $1 trillion. However dubious and wasteful, this enterprise has been internalized, becoming, in Washington parlance, a “self-licking ice cream cone,” and it will likely last as long as terrorism does. Since terrorism, like crime, can never be fully expunged, the United States seems to be in for a long and expensive siege.