“The Executive is NOT obligated to spend it.”
Actually, per the law indicated, he is.
The obligation is that it be completed by the end of fiscal year (a deadline which Congress explicitly extended for Trump, covering this particular spending).
It doesn’t matter what the law says. The constitution does not give the legislative branch that power. They can stipulate it be spent by a certain time - but they cannot force it to be spent.
The law doesnt say it has to be spent. It says if it is to be spent it must be spent by the end of the fiscal year. Otherwise you lose it. No obligation to spend it. Congress only allocates. Congress can rescind it as well if it chooses.
All this hyperbola would go away if people were still given a reasonable education in how govt works. But today we raise a bunch of ignorant gimmedats.