Ratings company Standard & Poor’s upgraded its outlook on the U.S. to “stable” from “negative” on Monday and said “tentative improvements” on the political and economic fronts have bought Washington extra time to grapple with long-term challenges. The move comes almost two years after S&P shook up Washington by becoming the first ratings company to remove the nation’s pristine “AAA” rating due to widespread concerns about soaring debt and deficit levels. But S&P affirmed its “AA+” credit rating on the U.S. on Monday and said the revised outlook to “stable” indicates the likelihood of a near-term downgrade is less than...