Republicans want to cap spending and revenues at percentages of GDP. This is an incredibly stupid and ignorant idea. Why ignorant? Because federal revenues and expenses are highly dependent on the business cycle - one of the hallmarks of capitalism. Times are good, revenues up, expenses down (less people collecting unemployment, people delaying taking social security), times are bad, revenues down, expenses up. This is a simple concept that it appears Republicans have never heard.
On the revenue side, corporate income (CI) and capital gains (CG) are highly business cycle dependent - much more so than individual income (II). Because CI & CG are bottom-line taxes - only profits are taxed, while II is top-line. By my rough calculation, this adds +- 2% OF GDP volatility to federal tax revenues.
On the spending side, unemployment expenses go up by about 1% of GDP from peak to trough, so +- 0.5% GDP added volatility. You have Medicaid and other means-tested programs that would also add volatility (incomes & unemployment go up, less people qualify, economy gets better, fewer people qualify) - these could add another +/- 0.5% GDP volatility.
These are only estimates, but it is not hard to get to a 6% GDP swing from peak to trough in the deficit - this is without any policy changes. Including policy changes, we've seen about 8-9% GDP delta, which makes sense for the cyclical + policy change elements.
The folly - evidenced by the W tax cuts - is that if you take a balance at the best point as the policy norm, you will have significant deficits in recessions - with IDENTICAL policies. Policy proposals that don't acknowledge the significant business cycle dependence of revenues and expenses aren't serious.