Actually, he must spend the bucks on what was authorized in the budget.
However, he can reprogram budget to fit the need of the nation and he can do that by submitting a reprogramming justification document/request, and it must be approved by the Senate.
That does not apply to discretionary funds not directly applied to any program. Those are what he allocated to the wall.
Nope. He can do it without any approval because he made an emergency declaration. That is the law. The law that was written and passed(Back in the 90’s I believe) gives congress the right to vote by 2/3rds vote to overrule the president. They tried that already and did not succeed. The judges on the 9th who made this ruling need to be slapped down by the USSC. They are not real judges. They have no respect for the law.