Having spent eight years accusing their Democratic colleagues of enabling a runaway president, congressional Republicans face a question: Will they fall in line when President Trump charts a course they oppose?

Congress can dominate domestic policy, but has a comparitively weak hand to play in foreign affairs. Trump’s campaign dovetailed with traditional GOP views in some areas, such as bolstering the military, so he need not always be at odds with congressional Republicans. In other cases — his apparent desire for a rapprochement with Russia, despite the ongoing aggression in Ukraine; his doubts about the utility of military partnerships with Asia-Pacific allies — they could be on a collision course. If and when that clash happens, the lawmakers will have to contend with a president who has broad power to set foreign policy without congressional approval, reinforced by his popularity in Republican congressional districts.