Republican Ted Cruz could cause the US to default on its debts.

How could this happen? Because the Senate can move quickly when necessary, but only by unanimous consent. Let’s say Harry Reid (D-Nev.) and Mitch McConnell (R-Ky.) strike a deal today (Monday) (that’s looking unlikely). Cruz surely won’t like it and has said repeatedly, “I will do everything necessary and anything possible to defund Obamacare.” If he’s true to his word, he could drag out the proceedings past Thursday and possibly well beyond. “If a determined band of nut jobs wants to take down the global economy, they could do it,” says Jim Manley, a former top staffer for Reid. “Under Senate rules, we are past the point of no return—there’s not anything Reid or McConnell could do about it.”

http://www.businessweek.com/articles/2013-10-14/ted-cruz-could-force-a-debt-default-all-by-himself