It isn’t daft. The Republicans since Reagan have pushed a fringe legal theory called the Unitary Executive Theory. Basically, they want the president to fully control the executive branch and military such that theirs is the only voice that matters for much of the government. Not unlike a king, but partially checked by congress and the courts. They have been taking (illegal) actions to try to get sued, and also have been suing others/other branches of government, to try to get the Supreme Court to hear cases that will support this fringe legal theory so that it becomes the law of the land.
I am not a lawyer, but this is possibly something Trump can legally do since he is Commander in Chief of the armed forces. However, this seems more like an apportionment thing, which is Congress’ responsibility. Congress has allocated funds to send military aid to Ukraine. So, even if Trump as Commander in Chief could say “no more weapons to ukraine”, it seems doubtful to me that he could (legally) stop weapons shipments currently en route.
But, by the time whatever government office sues the office of the president to get a judge to enjoin them to send the agreed upon weapons that were already apportioned, it will already have hurt Ukraine somewhat. Trump often weaponizes inefficiency. And these sort of illegal acts aren’t crimes per se - they’re just procedural breaches - the legal remedy is just to reverse the action.
So, probably not legal. But Trump gets to weaponize his administration’s incompetence (or feigned incompetence) to at least delay aid. More competent people may support these actions, knowing they’re illegal, to try and strengthen the president’s role even further.
This isn’t quite right. Trump didn’t really modify laws. That isn’t even something he can claim to do since he is the head of the Executive branch, not the Legislative one. He issued executive orders, many of which were illegal, and he had some cronies who enacted some of them anyway - others did not enact some of these, and others were not really actionable (like when he declared that no one has a gender). He did rescind many policies, but he can’t just make laws go away on his own. There are literally hundreds of court cases currently challenging these executive orders - seeing as how the judiciary is the primary check on the executive branch, that is the system working to check presidential power.
However, I am not a liberal, I am a socialist and do not think this is working well - there are many problems here. The highest levels of the judiciary have been largely captured by far-right judges, many of whom are specifically aligned with Trump’s goals and support the unitary executive theory. Also, this method of checking presidential power is extremely slow. For every illegal action Trump’s administration takes, a court case has to be crafted, filed, heard, and adjudicated. Every one. And invariably, some will not reach the correct outcome and others will never actually be taken to court - there are just too many.
Basically, the administration is using the fact that they control every branch of government to dismantle or capture core government agencies and to provide cover for various illegal actions - forcing them through if only temporarily for various political and structural ends. A soft coup, basically. So yeah, the fact that something like this is possible is proof of the flaws inherent in this system of government.