US and Israel said Iran's nuclear weapons research was a reason for war. Here's a look at the state of that program.

As the US-Israeli war with Iran carries on through its fourth day, some of the Trump administration's justifications for the war have shifted. But one objective has remained constant so far: Preventing Iran from developing a nuclear weapon, despite Trump claiming that US airstrikes obliterated" Iran's nuclear program last June. To better understand this specific US objective, The World's Marco Werman spoke to Darya Dolzikova. She's a nuclear proliferation expert at the Royal United Services Institute for Defence and Security Studies in the United Kingdom.