How close is Iran to producing a nuclear bomb?

The 2015 Iran nuclear deal is being eroded and now, efforts to revive it face a new challenge: the killing of Tehran's top nuclear scientist.

Let’s look at the deal and how close Iran could be to producing a nuclear bomb.

The accord is one of the most intrusive nuclear verification regimes imposed on any nation.

[U.S. President Barack Obama, saying:] "...A lasting, comprehensive deal that prevents Iran from obtaining a nuclear weapon while allowing it to access peaceful energy."

It has one objective: to extend how long it would take Tehran to get enough fissile material together to make a bomb, known as the “breakout time.”

Iran maintains that it has never sought nuclear weapons and never would and says its nuclear work only has civilian aims.

But Tehran began breaching the deal's curbs last year in a step-by-step response to Trump's withdrawal from the deal in May 2018, and the reimposition of U.S. sanctions.

[U.S. President Donald Trump, saying:] "We cannot allow the world's leading sponsor of terrorism to possess the planet's most dangerous weapons."

Iran exceeded the limits of how much enriched uranium it can stockpile, the enrichment level it's refined at, and the type of centrifuges and sites it uses for the process.

Tehran is still cooperating with the U.N. agency that polices the deal, which in turn says Iran isn’t moving ahead with nuclear work as fast as it could.

But the breaches means the “breakout time” has been shortened.

So how close is Iran to having a bomb? Estimates of the breakout time vary.

The aim of the deal was to increase it from around two to three months to at least a year.

But many experts say that’s conservative and Iran would, in reality, need longer.

Then, even if enough fissile material was accumulated, it would need to actually assemble a bomb and probably one small enough to be carried by its ballistic missiles.

It’s unclear how long that would take, but the stockpiling of fissile material is widely seen as the biggest hurdle in producing a weapon.

Supporters of the deal are hoping for a change in U.S. policy once President-elect Joe Biden takes office.

Biden has said he will return the U.S. to the accord if Iran resumes compliance.