Obama is referring to something that happened in 2011. When U.S. airstrikes in Libya aided rebels in the capture of dictatorial leader Muammar Gaddafi, Libya’s leader was executed. The government fell apart and the country plunged into chaos. Today, roughly 5,000 ISIS fighters reside in Libya. ISIS was able to gain a foothold when Gaddafi was killed and Obama says the U.S. didn’t have a plan to save the Libyan government. That was his biggest mistake as president.