In theory the Treasury Dept. gets the money from taxpayers but the Republicans left the government so far in debt and with unfunded infrastructure obligations that is a joke. They just funneled all the money that the government took in to their own pockets. If you voted Republican and you didn't get your share, better complain to the RNC.
So the Treasury Dept. is basically just printing the money. China is not going to lend us any more. They are trying as hard as they can to unload the Dollars they are holding while anybody will still take them.
Surprisingly, printing money to fund the Government isn't always a bad thing. The only trick is convincing people to accept it. If you can do that, it is far better than borrowing money from the fat cats sitting around the pool. Their money isn't "real" either but they expect us to pay them interest on it as if it were.
Even as bad as things are, if Obama's people know what they are doing, they can make this work out. Assuming that he isn't a secret Republican with a fake middle class birth certificate.