This link will help you understand Clinton's budget surplus. Clinton did not spend the surplus, and stated that he believes it should be used to pay for social security. Bush did not use it to pay for social security, but instead spent it as though it were part of his usual tax dollars.

The reason I say that it is generally better practice to use social security tax dollars to prevent debt is because interest on debt accumulates much faster than interest gathered on money invested. That is, if the government went into debt, it would lose more money than it made from the interest of investing the social security money, and this loss would eventually have to be repaid by the taxpayers in the form of increased taxes.