Shawn Tully worries about the coming debt crisis:

It can't go on forever, and it won't. What will shock America into action is the prospect of fiscal collapse, which will grow more vivid each year. In 2008 federal borrowing accounted for 41% of GDP, about the postwar average. By 2019 the burden will double to 82% by the CBO's reckoning, reaching $17.3 trillion, nearly triple last year's level. By that point $1 of every six the U.S. spends will go to interest, compared with one in 12 last year. The U.S. trajectory points to the area that medieval maps labeled "Here Lie Dragons." After 2019 the debt rises with no ceiling in sight, according to all major forecasts, driven by the growth of interest and entitlements. The Government Accountability Office estimates that if current policies continue, interest will absorb 30% of all revenues by 2040 and entitlements will consume the rest, leaving nothing for defense, education, or veterans' benefits.

To understand why a massive tax increase, probably a VAT, is the mostly likely outcome, it's crucial to look at what's driving the long-term, widening gap between revenues and spending.

Put simply, spending is following a steep upward curve, while revenues are basically fixed as a portion of GDP. Why? Because future spending is driven mostly by entitlements, which are programmed to rise far faster than national income, while revenues depend heavily on the personal income tax, which yields receipts that typically rise or fall with GDP. Under George W. Bush, the U.S. experienced a prelude to the crisis before us: Spending rose rapidly, while revenues remained reasonably flat. Bush created an expensive new entitlement, the Medicare drug benefit (cost this year: $63 billion), and let spending on domestic programs from education to veterans' benefits run wild. Over seven years the wars in Afghanistan and Iraq added a total of some $900 billion to the budget. All told, Bush raised spending from 18.5% to 21% of GDP, setting in motion a chronic budget gap by piling on new spending without paying for it.

The magnitude of the damage Bush did is still amazing. But when those tax increases come, they need to have his name attached to them. He made them inevitable; and deserves to go down in history for them.