Another historic use of this policy is whether the United States would retaliate to a chemical or biological attack with nuclear weapons; specifically, during the Persian Gulf War. Related is the notion of a nuclear umbrella. Some commentators believe President Barack Obama broke US policy and damaged U.S. interests by failing to take sufficient action against the regime of Bashar al-Assad for its Ghouta chemical attack on civilians in the village of Ghouta near Damascus on August 21st, 2013. President Barack Obama had used the phrase "red line" in reference to the use of chemical weapons on August 20th, just one day prior. Specifically, Obama said: "We have been very clear to the Assad regime, but also to other players on the ground, that a red line for us is we start seeing a whole bunch of chemical weapons moving around or being utilized. That would change my calculus. That would change my equation."