Congressional Republicans will defer to President Trump on many things, but on foreign policy, they are more willing to assert themselves. That’s been clear in the aftermath of Trump’s announced withdrawal from Syria and the resignation of Defense Secretary Jim Mattis. But a more subtle sign of the president’s loose grip on lawmakers was the emergence of an unlikely alliance against him that has been described by one of its participants as a sign of the “end times.” Sens. Lindsey Graham, R-S.C., and Rand Paul, R-Ky., represent opposite poles of the GOP foreign-policy spectrum. Graham is hawkish, insisting that if we do not fight America’s enemies “over there,” we will instead face them “over here.” Paul is a skeptic of military intervention, especially in the Middle East, who argues the U.S. is fighting too many wars with too little congressional authorization. On Saudi Arabia, the two of them are united: They want to punish Riyadh for the murder of journalist Jamal Khashoggi and are exasperated by the president’s unwillingness to confront Crown Prince Mohammed bin Salman. Trump wants to continue to have a close relationship with the Saudi regime, which he views as an important counterweight to Iranian influence in the region. Normally, the two senators are more likely to be hurling insults at each other than collaborating. Paul has called Graham a “warmonger” and a “danger” to national security. Graham rips the junior senator...