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.
Whether by "defunding" or by "refusal" to appropriate the law would be mortally wounded but there is little chance of either. Nevertheless, conservatives should soldier on and draw the battle lines clear for all to observe. Let the country divide on this issue rather than the mush we will get from Boehner and McConnell.