Obama controls the purse strings when it comes to disbursing tax revenues. He's already holding social security and military pay hostage, so why not tax refunds too.
Actually Congress does, but he calls the shot...that said if he hold back VA, SS, military etc etc pay it won't be the GOP or Congress that takes it in the shorts, it will be him, he is the one that will make the call.
Don't forget, the US Treasury has money pouring in every single day, we can pay our bills, we suddenly are not $1 T in the hole. We need to go into default and shift the blame on bammy, it will sink his ship....