Yields in the Treasury market are rising, threatening to make it more expensive for consumers and the U.S. to manage debt.

Moody's downgrade of the U.S. sovereign credit rating late Friday appeared to have a modest impact on corporate bond market activity on Monday, as spreads widened slightly and new bond sales started the week softer than expected.

After recovering from an initial jolt, U.S. stocks drifted through quiet trading following the latest reminder that the U.S government may be hurtling toward an unsustainable mountain of debt.