President Donald Trump's rejection of Saudi Crown Prince Mohammed bin Salman's appeals to launch strikes against the Houthis on Thursday has dramatically highlighted the kingdom's growing vulnerability — and isolation — in the face of a renewed Houthi campaign for control of the Bab al-Mandeb Strait. The crown prince telephoned Trump twice and was rebuffed both times, according to Axios, which broke the story.

The news, confirmed to Al-Monitor by a senior official based in the Gulf, came as the Iran-backed militant group reached the key island of Perim on Friday, at the narrowest point of Bab el-Mandeb. It followed Thursday's capture by the group of the strategic Red Sea port of Mokha from Saudi-backed pro-government forces, who failed to stem the Houthi advance despite sustained Saudi air support. The price of Brent crude rose to more than $105 a barrel, its highest price since July, following Mokha's fall.

Trump's reaction should not have come as a surprise, several regional officials speaking on background told Al-Monitor. American officials have said the administration has no plans to engage in direct military operations against the Houthis even as dozens of American military advisers remain on the ground in Saudi Arabia and concern mounts over the cascading effects of Houthi gains on the broader Iran conflict. CENTCOM head Adm. Brad Cooper traveled to Saudi Arabia on Thursday for what are being described as urgent coordination talks. But there is little indication that Washington will alter its stance, the sources said.

America has had no appetite for conflict with the Houthis since reaching an Oman-mediated deal with the group in May last year. The Trump administration agreed to stop bombing Houthi targets in Yemen in return for a Houthi pledge to stop attacking American vessels in Bab el-Mandeb and the Red Sea. "The understanding was that the Saudis would contain the Houthi threat on their own," one of the sources briefing Al-Monitor said. But the start of the Iran conflict in February upended those plans.