Led by talk of interest rate hikes and another North Korea Nuclear test, U.S. markets fell sharply. With almost six weeks of market calm, volatility came roaring back.

There was not much green in today's S&P 500 Stock Index.

Art Cashin, UBS Floor Director, discusses today's market sell-off and how the Federal Reserve is front and center. Watch it here on CNBC.

Brian Wesbury, First Trust Chief Economist, explains why he believes there is ample room for this bull market to continue. Read his analysis here in this week's Monday Morning Outlook.