Still, there have been government shutdowns in the past and the markets have quickly recovered. At the end of last year, Congress approved legislation that averted a series of tax increases and budget cuts known as the fiscal cliff. Stocks fell sharply in the days leading up to that agreement, but they rebounded quickly.
And in past debates over budget issues, investors were faced with other big crises that heightened the sense of risk, including the European debt crisis and a potential double-dip recession in the United States.
Since the beginning of this year, most other serious threats to the global economy have faded and Wall Street has habituated to relatively smooth sailing. The benchmark Standard & Poor's 500-stock index is up over 18 percent this year.
In recent weeks, the primary concern among market participants has been the Federal Reserve and its decision about whether to slow down, or taper, the bond-buying programs that have been used to stimulate the economy.
The Fed's decision to hold off on tapering was still the main topic of conversation on trading desks at the beginning of last week. But as the week went on, more and more investors began to tune in to the standoff between House Republicans and Senate Democrats. Stocks fell on Friday to close out the first down week in a month.
The main focus on Wall Street is the possibility that the government will stop making payment on its outstanding bonds when the current borrowing limit is reached, which is expected to happen on Oct. 17.
(Read more: Debt ceiling fight won't spur volatility—yet: Pro)
Treasury bonds are viewed as the bedrock of financial markets, thanks largely to the assumption that the United States will always pay its debts. Most analysts say that if that were thrown into question, the consequences would be catastrophic, and largely unpredictable.
"Even if it's a brief failure, it would forever be a signal to the market that you can't trust the United States government to make its payment when it's due," said Millan Mulraine, the director of United States research and strategy at TD Securities. "That would shake the foundations of the global financial system."
Before Congress can turn its full attention to the debt ceiling, it will first have to deal with a resolution to keep the government open when the new fiscal year begins on Tuesday.