Trump signed the new National Defense Authorization Act (NDAA) this week. Among other things, the bill contained provisions that place conditions on U.S. support for the Saudi coalition. The president made clear in his signing statement  that he was going to ignore any limitations  Congress tried to put on U.S. backing for the coalition’s war effort:
The signing statement singles out several provisions which Trump argues would restrict his control in ways he believes are needed for “military missions,” and inconsistent with his “constitutional authority as Commander in Chief.”
Trump suggested that he’d ignore all the limitations placed on the Yemen War, and objected to providing an assessment on war crimes to Congress, saying it violates executive privilege.
The attempt to put conditions on U.S. support for the war on Yemen was never likely to reduce military assistance to the coalition for the reasons I laid out here . The Secretary of State could very easily claim that the Saudis and their allies were meeting their requirements in order to continue U.S. military involvement, and nothing would change. The president’s signing statement confirms that the administration has no intention of paying attention to Congress’ conditions. Jeremy Konyndyk comments on this:
In plain English, this means the President does not see blowing up buses of Yemeni schoolchildren with US-built bombs and US-fueled planes as any reason to reconsider US support to the Saudis. https://t.co/vo7xEniQ8h 
— Jeremy Konyndyk (@JeremyKonyndyk) August 15, 2018 
U.S. involvement in the war on Yemen is unauthorized and illegal. Presidents Obama and Trump have illegally introduced U.S. forces into hostilities in Yemen in support of the Saudi coalition bombing campaign without Congressional authorization. Neither of them had the authority to do so. Congress needs to force an end to U.S. support, and that means revisiting the war powers challenge that it failed to make earlier this year. Nothing less will be a strong enough challenge to the administration’s indefensible Yemen policy. If they don’t challenge the legality of U.S. involvement in the war, Congress will continue to be ignored and overridden.change_me