[nathanbedford]

Of course Congress can ban Obamacare spending, whether entitlement or not, whether "mandatory" or not, otherwise one Congress could bind all succeeding congresses unto eternity.

[Vigilanteman]

Congress has also used its power of the purse to unilaterally cancel treaty obligations:

[Jim Noble]

Congress can only “defund” Obamacare IF the House and Senate both pass a bill doing that, and the President signs it.

The House, alone, can REFUSE to pass any bill appropriating money for Obamacare.