Stocks struggled on Monday, after Moody’s Investors Service slashed its U.S. credit rating outlook to "negative" from "stable." While the Dow managed a modest gain, the S&P 500 and Nasdaq both settled below fair value, as utility stocks continued to falter. With the bulk of earnings season now in the rearview mirror, traders are turning their attention to the big batch of inflation data that is due out later this week.