Moody's U.S. debt downgrade is raising concerns that investors could reevaluate their appetite for U.S. government bonds, with the potential for rising yields to put pressure on stocks that are trading at elevated valuations.

Stocks slumped at the open of trading on Monday after a downgrade of U.S. credit triggered a spike in debt yields that threatened to raise borrowing costs throughout the nation's economy. The Dow Jones Industrial Average dropped 295 points, or 0.7%, while the S &P 500 fell 0.9%. The tech-heavy Nasdaq plunged 1.2%.

All three major U.S. stock market indexes rose Monday afternoon, following an earlier selloff sparked by long-dated Treasury yields surpassing the 5% mark after the financial ratings agency Moody’s downgraded the U.S. government’s credit rating late last week, citing rising debt and interest payment ratios.