Michael Morell was acting director and deputy director of the Central Intelligence Agency from 2010 to 2013.

It is conventional wisdom that North Korea is not yet able to put a U.S. city at risk of nuclear attack. Air Force Gen. Paul Selva, vice chairman of the Joint Chiefs of Staff and the country's No. 2 military officer, captured this view in a statement last week to Bloomberg News. Selva said: "It is clear North Korea has the capability to build a missile that can range the distance to the United States, but North Korea has yet to demonstrate it has the requisite technology and capability to actually target and strike the United States with a nuclear weapon." Many other U.S. officials, as well as outside experts, have made similar comments.

I think the conventional wisdom may be wrong. I believe that North Korea may have the capability today to successfully conduct a nuclear attack on the United States. I believe that the conventional wisdom may be based on a fundamental mistake of logic: Just because North Korea has not yet demonstrated a capability does not mean it does not have it.

What is the case for concluding that North Korea may already have the capability? There are three key pieces. First, North Korea's first unambiguously successful nuclear test was in 2009. (North Korea's first test, in 2006, most likely failed.) The 2009 test showed that North Korea could generate a nuclear yield from a device. And that test has been followed by four other successful nuclear tests — the latest being this past weekend. The explosive yields of the tests have grown over time.

Second, in December 2012, North Korea successfully put a satellite in orbit with a rocket that, had it been a missile, could have ranged to at least Alaska and, if more work had been done, could have hit the contiguous United States. In addition to the range, the satellite launch demonstrated that North Korea can successfully separate a payload from a rocket or missile. North Korea, of course, has since demonstrated, with two intercontinental ballistic missile tests this summer, that it has missiles capable of ranging as far east as Chicago.

Third, and this addresses the pieces of the puzzle that we have not seen, I believe that North Korea has the technical capability and has had the time necessary to make a nuclear weapon small enough to fit on a long-range missile and to ensure that the warhead can survive the vibrations, pressures and heat of reentry. If you can build a nuclear weapon, you can make the rest of the pieces work.

I am not the only one to express the view that North Korea might already have the capability to put a U.S. city at risk. At an October 2016 Council on Foreign Relations event, then- Director of National Intelligence James R. Clapper Jr. told Charlie Rose, "We ascribe to them the capability to launch a missile that has a weapon on it that could reach parts of the United States, certainly including Alaska and Hawaii." In response to a follow-up question, Clapper added, "We've assessed . . . for years that they could do it."

A year earlier — at an Atlantic Council event in October 2015 — Adm. William Gortney, then-commander of U.S. Northern Command, said, "I agree with the intel community that we assess that they have the ability, they have the weapons, and they have the ability to miniaturize those weapons, and they have the ability to put them on a rocket that can range the homelands." As commander of Northcom, Gortney was responsible for protecting the country from a missile attack.

Why is this such an important issue? Because, if you believe, as Selva and others apparently do, that North Korea cannot yet attack the homeland with a nuclear weapon, it follows that the United States can take preemptive military action against North Korea without risking a retaliatory nuclear strike by Pyongyang. You can take such action without putting the United States at risk.

However, if you believe, as I do, that North Korea might be capable of striking us today, it follows that a preemptive U.S. military strike against Pyongyang could bring about the very thing that we are working to avoid — the nuclear annihilation of a U.S. city and the deaths of millions of Americans. If this darkest of scenarios were to play out, the assumption and assessment that North Korea cannot yet threaten us would be a strategic mistake of historic proportions.