The United States and European nations agreed Saturday to impose the most potentially crippling financial penalties yet on Russia over its unrelenting invasion of Ukraine, going after the central bank reserves that underpin the Russian economy and severing some Russian banks from a vital global financial network.The United States and European nations agreed Saturday to impose the most potentially crippling financial penalties yet on Russia over its unrelenting invasion of Ukraine, going after the central bank reserves that underpin the Russian economy and severing some Russian banks from a vital global financial network.