He wasn’t there. And yet he was. He was in the answers about the economy. He was in the language about the Deep State. He was the target of blistering criticism, even on Washington spending during his administration. His shadow was long — every candidate on Wednesday’s Republican debate stage referred to him or his signature issues — and the themes were his: American decline, immigration, China, political correctness, the homelessness and crime rates in Democratic-ruled cities. One of the candidates, businessman Vivek Ramaswamy, even employed the signature Trump critique of climate change: “hoax.” Donald Trump’s name was written in...