Citi analyst Scott Gruber downgraded U.S. Silica Holdings to Neutral and cut his price target for the shares to $28 from $43. The company's free cash flow outlook "evaporates" the bull case, Gruber tells investors in a post-earnings research note. While peers continue to guide for higher realized pricing, U.S. Silica "appears to be trading lower margins in 2018 to mitigate downside risk in 2019 and beyond," the analyst contends. He believes this strategy removes two key catalysts near term, namely positive EBITDA revisions and free cash flow enhancing the cash return program.