By Alexandra Ulmer and Jarrett Renshaw (Reuters) – The month of May brings Donald Trump the biggest test of his political clout since the end of his presidency, as candidates he has endorsed contest Republican primaries that will set the stage for November’s midterm congressional elections. Trump-backed candidates in Ohio, Pennsylvania and North Carolina face active and well-funded challengers seeking the Republican nomination to run for U.S. Senate. The former president has also backed a challenger to Georgia’s sitting Republican governor, who angered Trump by rejecting his false claims that …