Washington — CBS News projects Rep. Julia Letlow and Louisiana state Treasurer John Fleming advanced to a runoff in Saturday's Senate Republican primary, knocking out incumbent GOP Sen. Bill Cassidy.  Cassidy, 68, was one of seven Senate Republicans who voted to convict President Trump in his impeachment trial after the Jan. 6 attack on the Capitol in 2021. And although he's emphasized his cooperation with the administration in recent years, the president endorsed Letlow in January, encouraging