Many economists believe government deficits influence the economy through the loanable funds market, whose existence Chartalists and other Post-Keynesians dispute. Government borrowing in this market increases the demand for loanable funds and thus (ignoring other changes) pushes up interest rates. Rising interest rates can "crowd out" (discourage) fixed private investment spending, canceling out some or even all of the demand stimulus arising from the deficit—and perhaps hurting long-term supply-side growth. But increased deficits also raise the amount of total income received, which raises the amount of saving done by individuals and corporations and thus the supply of loanable funds, lowering interest rates. Thus, crowding out is a problem only when the economy is already close to full employment (say, at about 4% unemployment) and the scope for increasing income and saving is blocked by resource constraints (potential output). Despite a government debt that exceeded GDP in 1945, the U.S. saw the long prosperity of the 1950s and 1960s. The growth of the "supply side", it seems, was not hurt by the large deficits and debts.
A government deficit increases government debt. In the U.S., the government borrows by selling bonds (T-bills, etc.) rather than getting loans from banks. The most important burden of this debt is the interest that must be paid to bond-holders, which restricts a government's ability to raise its outlays or cut taxes to attain other goals.
Other articles related to "loanable funds, funds":
... The "rate of return on capital" is taken into account when determining the demand for loanable funds ... as the rate of return on capital is greater than or equal to the interest rate on paid on funds borrowed, firms will continue to demand loanable funds ...