If Washington's leaders need a reason to get serious about the long-term-deficit problem—now—here it is.

As the U.S. figures out how to lower its deficit, it does so at a time when it's paying $200 billion in interest in 2011 alone. WSJ's Gerald F. Seib foreshadows bad times ahead if Congress doesn't immediately make inroads into the deficit.

There is a cancer eating away at the budget from within, one that steadily drains American wealth, sends much of it overseas and only gets worse over time. It is the interest America pays on its national debt.

This year the U.S. will spend more than $200 billion—roughly the gross domestic product of Chile—merely paying off that interest. That's nearly as much as it will spend to provide health care to poor citizens through the Medicaid program.

By comparison, the spending debate now raging in Washington, over whether to cut discretionary programs by $20 billion or $60 billion this year, is about chump change, and misses the real long-range threat almost entirely.