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 closed largely unchanged on Monday despite a downgrade of U.S. credit, which triggered a spike in debt yields and threatened to raise borrowing costs throughout the nation's economy. The Dow Jones Industrial Average closed up 137 points,