If Treasuries were ejected from the market, "Well, holy cripes," Kochan said in an interview.
In 2011, the last time Congress was gridlocked over the extension of the debt ceiling, repo rates rose as money-market funds pulled back because they didn't want the risk of holding a security in default.
"A lot of this is about fear of the unknown," said Scott Skyrm, a former head of repo and money markets for Newedge USA and author of "The Money Noose: Jon Corzine and the Collapse of MF Global." "There is no upside to being in the market in that environment, so people pull out."
The United States didn't default on its debt in 2011. Republicans and Democrats reached a last-minute deal to raise the borrowing limit. Even so, the posturing hurt consumer confidence and wiped out $6 trillion of value from global stocks.
While none of the people interviewed for this story expect the world's largest economy to default this time either, most say the chances of it happening now are higher than in the past.
"It would be insane to default, but it's no longer a zero- percent probability," said Simon Johnson, a former chief economist of the International Monetary Fund who teaches economics at the Massachusetts Institute of Technology and is a columnist for Bloomberg View.
The U.S. hasn't defaulted since 1790, when the newly formed nation deferred until 1801 interest obligations on debt it assumed from the states, according to "This Time Is Different," a history of financial crises by Carmen Reinhart and Kenneth Rogoff.
In 1979, the U.S. was late to make payments on about $122 million of bills, in part because of "severe technical difficulties" that the Treasury said stemmed from a word- processing failure, according to the Financial Review's August 1989 issue. While payments were made after a short delay, including with interest for tardiness, the hiccup caused yields to rise by half a percentage point and stay there for months.