Mitt Romney, in his latest attempt to help stop Donald J. Trump, joined Gov. John Kasich of Ohio on the campaign trail on Monday as Mr. Kasich tries to pull out a victory in his home state. At an air museum between Akron and Canton, where Mr. Kasich’s campaign bus pulled in next to a World War II-era bomber, Mr. Romney highlighted Mr. Kasich’s experience in Congress and as Ohio’s governor. “Unlike the other people running, he has a real track record,” Mr. Romney said in introducing Mr. Kasich at the town hall style event. “He has the kind of...