A bomb blast in Syria kills an American service member, leading to questions about how long the U.S. will remain in the war-ravaged country. Russian diplomats are forced out of countries around the world in response to the poisoning of a Russian ex-spy in London. Plus -- another administration shake-up in Washington, as David Shulkin is ousted from the Department of Veterans Affairs. CBS News Correspondent Steve Dorsey will have these stories and more on the CBS News Weekend Roundup.