Q. Why Is it Potentially Catastrophic for the Government to Default?
A. In part because the repercussions would be felt worldwide by a global economy that still isn't at full health. Banks in the United States and overseas use Treasurys as collateral when they borrow from each other. If Treasurys were no longer seen as risk-free, it would disrupt borrowing and jolt credit markets. A financial crisis like the one in 2008 could follow.