Western diplomats who know the prince — known as M.B.Z. — say he is obsessed with two enemies, Iran and the Muslim Brotherhood. Mr. Trump has sought to move strongly against both and last week took steps to bypass congressional opposition to keep selling weapons to both Saudi Arabia and the United Arab Emirates.

“M.B.Z. has an extraordinary way of telling Americans his own interests but making it come across as good advice about the region,” said Ben Rhodes, a deputy national security adviser under President Barack Obama, whose sympathy for the Arab Spring and negotiations with Iran brought blistering criticism from the Emirati prince. When it comes to influence in Washington, Mr. Rhodes added, “M.B.Z. is in a class by himself.”

Prince Mohammed worked assiduously before the presidential election to crack Mr. Trump’s inner circle, and secured a secret meeting during the transition period with the president’s son-in-law, Jared Kushner. The prince also tried to broker talks between the Trump administration and Russia, a gambit that later entangled him in the special counsel’s investigation into foreign election interference.