What the graph says to me is that there is a rising trend in revenue which makes sense since the population grows and the per capita income grows. So there is an upward trend that asserts itself no matter what else happens. The question is, from what base does this upward trend begin?
Clinton set a base with his tax increase of 93 that led to a surplus by the end of his second term. Given that the year 2000 was near the top of the business cycle it is likely that if we had done nothing to change it, the fiscal balance would have bounced around near that balance point, sometimes negative and sometimes positive (THis, by the way, is what we should all wish for)
Bush cut taxes drastically and the revenue curve accordingly took a dip after which the usual long term trend reasserted itself. Note that this trend reasserts itself whether or not the taxes were cut, raised, or left the same - This much is clear in your graph.
Essentially then, Bush's cuts reset the base from which the underlying long term trend would grow - but now with a built-in gap between revenue and expenditure. Sure, the gap narrows on a business cycle upswing (as the graph shows over the last 3 years or so) but it will widen on a downswing (as is happening now and predicted to worsen over the next year.) but on average we now have a structural deficit.
The usual Republican response is to cut spending. Well, OK but the problem is that you could cut out ALL (100%) of non-defense discretionary spending and you would STILL have a deficit. Lets be really clear about this (and go to the bipartisan concord coalition site if you dont believe me - it is run by both repubs and dems who share a hatred of fiscal deficits) You cant eliminate the deficit through spending cuts alone. It is arithmetically impossible. You would either have to cut the military or cut entitlements to make it happen.
So, those who want to balance the budget with spending cuts, if you are honest about it, then tell us what exactly you want to cut. Here is a fun website that lets you experiment with exactly that
Penny Game Test Page