Reference for USAID note:
USAID was created by EO by JFK but it was made official in 1998:
“(a) In general
Unless abolished pursuant to the reorganization plan submitted under section 6601 of this title, and except as provided in section 6562 of this title, there is within the Executive branch of Government the United States Agency for International Development as an entity described in section 104 of title 5. (emphasis added)”
which means it was set by Act of Congress and therefore requires Congress to dissolve it. “Trump and Musk” don’t have that power. But once locks are put on the doors and people move on to other jobs, it’s hard to put the genie back in the bottle and get it started again.
Hence why Musk + Trump are acting with such speed. These actions will get overturned as illegal but it won’t matter by then.