Indiana’s primary will test President Donald Trump’s enduring power over the Republican Party as he tries to dislodge state senators who refused to go along with his call to redraw the state’s congressional map. Twenty-one Republican senators voted against redistricting in December, including eight running for reelection this year. Trump has endorsed primary challengers against seven, and the president’s allies have spent millions of dollars on races that rarely get much attention from Washington. It’s become a costly and unprecedented intraparty battle that has exacerbated tensions among Republicans ahead of the November midterm elections that will determine control of Congress. Indiana Lt. Gov.…