Robert Merry sums up Trump’s weakness:

He is merely a battery of impulses, devoid of any philosophical coherence or intellectual consistency.

The president could hardly be anything else, since the only things that seem to concern him are how others treat him and the status of his brand. He makes no firm commitments, and he reverses himself according to whatever is most expedient to him at the time. It is almost inevitable that he is winging it because he has no relevant experience or knowledge that would keep him from doing so. Trump believes in himself and nothing else, and Chesterton observed long ago that asylums were full of such people.

If Bannon et al. thought they could use him as a vehicle to advance their agenda, they failed to see that he was using them only as long as they could be valuable for helping him. The trouble for many Trump supporters is that Trump has never believed in any of the things they thought he represented, and so they were backing a leader who had no intention of risking anything on their behalf. This was especially true on matters of foreign policy, where Trump’s instincts for plundering and bullying could easily be directed toward conventional hawkish goals if they weren’t already heading that way. Merry sums up the results of Trump’s foreign policy thus far:

On foreign policy he has belied his own campaign rhetoric with his bombing of Syrian military targets, his support for Saudi Arabia’s nasty war in Yemen, his growing military presence in Syria, his embrace of NATO membership for Montenegro, his consideration of troop augmentations in Afghanistan, and his threat to consider military involvement in Venezuela’s internal affairs.

Trump has certainly governed as more of a conventional hawk than his campaign suggested he would, but his actions have been quite consistent with the blundering aggressiveness that he has displayed for years. His support for the war on Yemen, for example, is entirely in keeping with the rather deranged view that Obama was not pro-Saudi enough. Even though Obama backed the war on Yemen to the hilt for years, Trump was always going to be more supportive and less critical because he faulted Obama for not backing so-called “allies” as much as he should have. On NATO expansion, Trump doesn’t care if the alliance takes on new and unnecessary members. All that interests him is whether they pay what they supposedly “owe,” and even if they don’t he doesn’t seriously propose dissolving the alliance or withdrawing from it. As for Syria, his decision to order an attack on their government lines up with his contempt for international law and his desire to seem “tough.” He has no problem initiating illegal hostilities against other states, but he doesn’t like it when the U.S. is expected to clean up the mess afterwards.

Trump’s foreign policy has become almost entirely one favored by Republican hawks because the president doesn’t hold firm convictions on these issues and yields to what his hawkish advisers want. He has accepted a foreign policy of endless war because he is too weak and self-serving to pursue any other course.