@csgordon@zirk.us @gwaldby

The act of Congress authorizes spending.
It does not require spending, since that would be a violation of the constitutional separation of power.

Congress effectively says that the president may spend money out of the Treasury, but if the money doesn't exist in the Treasury anyway, then the law is moot.

If I tell you that you can spend up to $1,000 out of the cash in your wallet, but you only have $20 in there, then you can spend 20. There's no conflict there, no contradiction, I have authorized you to spend a bunch of money but it's a ceiling that is subject to what is actually available to spend.

So no, under the Constitution the Congress cannot obligate the executive branch to spend money. It is an equal branch, not a subservient branch. Congress can authorize, as per the Constitution, but it can't actually spend for itself.