RABAT—U.S. Secretary of State Antony Blinken sought to assure Gulf monarchies on Tuesday that Washington is determined to help them fend off attacks from the Iran-aligned Houthi group in Yemen. Blinken met with Abu Dhabi Crown Prince Sheikh Mohammed bin Zayed al-Nahyan, de facto ruler of the United Arab Emirates, in Morocco as part of a trip to the Middle East and North Africa. Washington’s Arab allies chafe at what they see as declining U.S. commitment to security in their region in the face of Iranian involvement in Yemen, Iraq, Syria and Lebanon which has nudged them into common cause with former arch-foe Israel. Unusually for a U.S. secretary of state, Blinken’s trip did not include any stops in Gulf monarchies or talks with Saudi officials. “We have real challenges to confront together, in the region and beyond,” Blinken said at the start of the meeting with Sheikh Mohammed at …