Susan Collins
US Senator from Maine
Mitt Romney
U.S. senator from Utah, former Massachusetts governor
George W Bush
43rd US president, ex-governor of Texas, son of George H W Bush
Tom Carper
US Senator from Delaware (2001-present); former US Rep from Delaware (1983-1993)
Tommy G Thompson
Lobbyist; former Secretary of Health and Human Services under Goerge W Bush; former governor of Wisconsin
Scott P Brown
US ambassador to New Zealand, former Republican US Senator from Massachusetts