In near-daily briefings with top military officials at the White House, President Donald Trump has reviewed options that include sending American troops into Iran. The decision whether to go ahead is perhaps his most difficult of the war since US strikes began February 28. For many Trump allies in Washington, the deployment of thousands of US troops to the Middle East would mean the swift end of their public support for the war— and likely threaten the administration’s ability to deliver the hundreds of billions of dollars in supplemental funding the White House will soon seek. But for Trump, fully...