Trump threatens to upend GOP agenda, Senate race with Louisiana endorsement

President Trump is giving Senate GOP leaders a large headache with his determination to endorse Rep. Julia Letlow’s (R-La.) Senate run implicit Sen. Bill Cassidy’s (R-La.), tossing caller uncertainty implicit cardinal parts of their docket and upending the contention successful a reddish state.   Trump preemptively backed Letlow’s Senate run implicit the weekend. The determination roiled…