Only Congress can create or dissolve a federal agency, department, or program. Only Congress can authorize funding or cut funding. The Executive does not have the legal power to withhold funds that Congress has authorized. Trump and Musk are guilty of obstruction of government operations and in violating the Congress's constitutional powers. It is a massive abuse of executive powers.
So Trump and Musk are engaging in illegal and unconstitutional actions. The question is, what do we do about it? Musk does not have Presidential immunity, so perhaps the defiant remaining FBI Agents should seek a warrant for the arrest of Elon Musk on these sort of charges. It must be done quickly before the situation gets worse.
Furthermore, the doctrine of Presidential immunity must be challenged again in the courts. I would assert that illegal and unconstitutional acts by the President and his agents can not by definition be "official". Therefore, the President and his agents do not have immunity from prosecution for these unofficial and illegal acts.
The most immediate response to all of this should be by the Democrats in the Congress. They need to clearly state that Trump and his agents are engaged in illegal and unconstitutional acts, these are high crimes and misdemeanors, and that the Republicans in the Congress must join them in the only immediate remedy to an illegal Presidency-- Impeachment. If the Republicans refuse to support an Impeachment, they will demonstrate their unfitness for office and this can be used against them in the next round of elections in 2026, if the Republic manages to survive until then.