This can be done by printing money, but more ususually (and sanely) is to increase Federal borrowing. The money is spent directly through Federal appropriations on specified budget items.
Isn't this theory, however, related directly to running a brief deficit and spending it on things of substance like hospitals, schools, etc. - and then in "good" years, paying off the deficit when there's a surplus?
Forget for a moment that the "budget surplus" of the last couple of Clinton years was largely illusionary. Assume that it were true. Every bloody member of Congress started salivating at the chance of spending every last dime of whatever part of that so-called surplus on whatever they could get their hands on.