President Trump has repeatedly attacked German Chancellor Friedrich Merz for comments he made about the U.S. role in the Iran war , targeting a leader who has worked hard to be in the president’s good graces and a country considered to be one of the U.S.’s strongest allies. ​The comments escalate Trump’s attacks on European nations that have not volunteered to back the U.S. in the conflict, which is unpopular in Europe and has taken a heavy economic toll on Germany and other countries by driving up energy costs. The war itself is dragging on Trump’s popularity, while creating a conundrum for Republicans in a midterm election year by exacerbating voter concerns about the economy. Merz had cultivated a positive relationship before this past week’s turn, and experts said he likely didn’t mean to cause a spat that has appeared to weaken any ties he has — or hopes to have — with the U.S. leader by speaking of the U.S. being “humiliated” by Iran.…