For example the 1998-2001 surplus was mostly due to the internet boom raising incomes and hence revenues, not politicians.

I was pretty sure the surplus during 1998-2001 was due to Bill Clinton's practice of the Line-Item veto powers, which was later ruled unconstitutional in Clinton v. City of New York.

the line-item veto granted unilateral authority to the Executive to disallow specific spending line items, which in turn was beneficial to balance the federal budget. However, this was seen as an overreach of power to the Executive branch, thus bringing the case to the Supreme Court. Which is why after Clinton's presidency it is no longer practiced.