Getting a substantial deal matters as much for financial markets as the political future of the U.S. political leaders. Standard & Poor's has said it would lower its AAA rating on U.S. government debt if it believes any deficit-reduction agreement is inadequate or the triggers put in place aren't credible. A lower rating would immediately boost borrowing costs for the U.S., businesses and households, harming the recovery and roiling financial markets worldwide.

"What we mean by credible is something that we think people are actually going to do," David T. Beers, managing director of sovereign and public finance ratings for S&P, said in a recent interview.

John Fath, managing partner for BTG Pactual, the large Brazilian investment bank said, "If I was a foreign holder of U.S. debt, I'd be asking myself, 'Who is running that country anyway? This is like riding on a motorcycle and steering it right in front of an 18-wheeler. Are they out of their minds?'"