British Prime Minister Theresa May on Wednesday showed she was siding with Present Trump at the NATO summit in Brussels, saying her country was paying its fair share for the defense alliance. “We lead by example, not only by meeting the NATO targets of spending 2 percent of our GDP on defense,” Mrs. May said, adding that the U.K. also deploys thousands of troops to NATO missions around the world. Mr. Trump has made cost sharing a top issue at the summit. He has been pressing for all 29 member nations to pony up the 2 percent of GDP, which is the level agreed to in 2014. The U.K. is among a handful of NATO countries siding with Mr. Trump as he shakes up the military alliance. Most of the allies are rankled and riled by Mr. Trump’s demand that they pay up.