National Security Adviser Jake Sullivan said Sunday Russia could resort to using chemical weapons in its war against Ukraine. Sullivan told Face The Nation host Margaret Brennan that Russia has gotten frustrated by the lack of movement by Russian forces into other parts of Ukraine, putting “extreme tactics” like chemical weapons on the table. “One of the reasons they’re not advancing, the central reason is the bravery and skill of the Ukrainian people, but they are being supported by substantial amounts of military assistance from the United States and our allies,” Sullivan said. He also would not say whether the U.S. would engage its military if Russia were to use the weapons, pointing back to President Joe Biden’s warning it would “pay a severe price.”