Moody's downgrade of the U.S. credit rating made it the third of the three major ratings agencies to downgrade U.S. credit since 2011 amid widening budget deficits.

The Moody’s announcement sent the yield on a 30-year Treasury bond to a high of 5.01% at one point on Monday. Bond yields rise as bond prices fall. When a selloff hits and demand for bonds dries up, it sends bond prices lower. In turn, bond yields move higher.

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.

Moody’s Ratings has joined Fitch Ratings and S&P Global Ratings as the last credit agencies to downgrade the U.S. economy, the world’s largest. The agency cited the country’s

If the U.S.’s loss of its final perfect credit rating boosts yields on Treasury debt, it likely would boost the cost of borrowing for both companies and consumers.

The U.S. government is spending far more than it takes in as revenue, causing ever-rising debt — and there is no sign that will change anytime soon. The big picture: Those facts are well-known to anybody who has taken a cursory look at the government's books.

CNBC's 'Mad Money' host and veteran market commentator Jim Cramer has urged investors not to get nervous in the face of concerns like the Moody’s downgrade of U.S. debt . The U.S.'s rising debt stands at $36 trillion as of now.