Yellen warns of 'calamity' unless Congress raises the debt limit. What's the holdup?

Treasury Secretary Janet Yellen leaves a meeting on April 21. She warns that economic chaos will ensue if Congress doesn't raise the debt ceiling in the coming weeks. (Alex Wong/Getty Images)

The U.S. government could default on its debt in a matter of weeks if it doesn't raise the debt ceiling.

That would spell "economic calamity," Treasury Secretary Janet Yellen warned this weekend.