The cartoon of a bomb that Israeli Prime Minister Bibi Netanyahu displayed two weeks ago at the UN has become a target of ridicule. Israeli online parodies hammered the prime minister.  

In the debate sparked by Netanyahu, three issues need to be separated and examined individually, each on its own merits.  First, what about the cartoon? Can we identify a better picture for conveying his message about Iran’s nuclear threat?  Second, was he correct in claiming that Iran is on the verge of completing 90% of the work for its first nuclear bomb?  Third, was it appropriate to draw the red line asserting that Iran must be stopped before it acquires even one bomb’s worth of 20% enriched uranium?

The question about the graphic naturally invites a competition.  As an entry in that contest, I include a graphic I presented this time last year as a way to simplify an essential truth.  For many observers, the difference between 5% and 20% enriched uranium appears to be a distinction without a difference.  But the difference really matters.  When a state has enriched uranium to the 5% level (used in fuel for a civilian nuclear electricity plant), it has done seven-tenths of the work to produce bomb-usable material.  When 5% material is enriched further to 20%, nine-tenths of the work and time required to make bomb-usable material has been completed.  That was the point the prime minister was trying to make – and that point is correct.  

In the metaphor of American football, enriching uranium to 5% is equivalent to Iran’s marching 70 yards down the field to our 30 yard line. Enriching to 20% drives into the red zone, down to the 10 yard line, completing nine-tenths of the work to make the material for a bomb. However dangerous it is to have an opponent 30 yards from one’s goal line, every serious fan knows that finding an opponent on the 10 yard line is many times worse.  

What about the prime minister’s claim that Iran is on the verge of enriching enough material to the 20% level that would take it nine-tenths of the way to bomb-usable material for a first bomb?  On this point, again, Netanyahu is essentially correct: Iran should have enough 20% uranium to re-enrich for a first bomb within about six months.  

Nonetheless, this issue is more complicated.  Iran claims that it is enriching to the 20% level is to produce fuel for its research reactor—which does in fact require 20% enriched fuel.  Consistent with Iran’s story, over the past year, it has diverted about half of its stockpile of 20% enriched uranium for fabrication into fuel for its research reactor.  At the same time, however, it has tripled the number of centrifuge lines producing more 20% uranium. Since it has already produced enough fuel for the research reactor to operate for at least six years, the rest of us are right to worry about what it intends to do with the additional 20% enriched uranium.  

Where then should a clear red line be drawn?  At the UN, Netanyahu drew that line at one bomb’s worth of 20% enriched uranium.  He claimed that once Iran has this amount, it could break out in a dash to complete enrichment and construct a bomb.

That argument is not persuasive. Iran’s stockpile of enriched uranium is currently under surveillance by IAEA inspectors.  If Iran ejected the inspectors in a crash program to complete production of bomb-usable material at its declared facilities, it would then also have to (1) convert that material into uranium metal, (2) assemble the other components of a weapon, and (3) test the bomb.

Ejecting the inspectors would sound a shrill alarm.  Israel and the U.S. would have several months to act.  And they would have a credible justification for attacking.  

Moreover, what state would produce enough material for just one bomb, test it to demonstrate the capability, and imagine that it had improved its security? Only a country that was inviting attack.

If Iran attempts to cross the goal line to a bomb, it will wait until it has amassed enough material for a half-dozen bombs—allowing it to test one and credibly claim to have a nuclear deterrent against attack.  On the current trajectory, Iran will not have enough 20% enriched uranium for a half-dozen bombs for at least two years.  

Netanyahu’s cartoon oversimplified the Iranian nuclear threat.  That should not, however, cause us to miss the central message he was attempting to send.  Iran has marched 90 yards down the field toward the goal line of a bomb.  It has done this in the face of the best efforts at sanctions and sabotage that the U.S. and Israel have been able to devise.  While sanctions have battered Iran’s economy, so far its nuclear program has not been blown off course. The time to intensify the search for realistic alternatives, or supplements to the current strategy, is now.  

Harvard University Professor Graham Allison is director of the Belfer Center for Science and International Affairs at Harvard Kennedy School.