Sometimes he works behind the scenes to try to contain the damage, but rarely drops any hint of his opposition in public.
After Mr. Trump abruptly declared in December that the United States would soon withdraw its 2,000 troops from Syria, the defense secretary, Jim Mattis, resigned. But Mr. Pompeo told aides the withdrawal was the president’s prerogative and defended it as a “change in tactics, not in mission.”
Still, he is not always in step with Mr. Trump. He has pushed ahead with sanctions against Russia, and in Poland, he watched American and Polish troops in a live-fire exercise near the Russian border — an unsubtle message to Moscow not to test the North Atlantic Treaty Organization.
But generally, Mr. Pompeo, a strong partisan and ideologue, aligns with Mr. Trump. In a scathing nationalistic speech in Brussels in December, Mr. Pompeo criticized institutions the United States helped create to maintain its global power — the United Nations, European Union, World Bank, International Monetary Fund and World Trade Organization.
In a January speech in Cairo, Mr. Pompeo attacked the policies of President Barack Obama. There has been little, if any, precedent for such a broadside of former administrations from a sitting secretary of state. Mr. Pompeo was widely criticized for it. By contrast, he praised President Abdel Fattah el-Sisi, Egypt’s repressive leader. He did the same with two other leaders who critics say have authoritarian tendencies, President Jair Bolsonaro of Brazil and Prime Minister Viktor Orban of Hungary.
On major issues, “the president is working to undermine us, and if Secretary Pompeo is supporting that, this is a fault,” said R. Nicholas Burns, an under secretary of state under President George W. Bush and a Harvard professor whom Mr. Pompeo has consulted.
“He’s an institutionalist, and he’s done some things well, starting with reinvigorating the State Department after Rex Tillerson dismantled so much,” Mr. Burns said, referring to the president’s first secretary of state. “But on policy, he has been the voice of unilateralism, of ‘our way or the highway.’ And he’s discovering, just recently, that the world is pushing back.”