Trump's endorsement power faces new test in Louisiana Republican Senate showdown

President Donald Trump's immense clout over the GOP and the power of his endorsements in Republican nomination races faces its latest test Saturday, as Louisiana holds primary runoff elections for the U.S. Senate.

Six weeks after denying Trump-targeted GOP Sen. Bill Cassidy a third six-year term in the Senate, Republican voters in the solidly red Gulf Coast state will choose between Rep. Julia Letlow and state Treasurer John Fleming for the now open seat.

A Letlow victory in the GOP...