U.S. stock benchmarks dropped at the start of a shortened session on the eve of the Christmas holiday, as comments from Treasury Secretary Steven Mnuchin sparked worries about bank liquidity. The Dow Jones Industrial Average DJIA, +0.19% opened 0.5% lower at 22,333, while the S&P 500 SPX, +0.29% started the day 0.4% down at 2,407. The Nasdaq Composite Index COMP, +0.36% kicked off 0.4% lower at 6,309. U.S. stock exchanges will end trading early, at 1 p.m. Eastern time, and will be closed on Tuesday for Christmas. In an apparent effort to calm markets after last week's equity selloff, which saw the worst weekly decline since 2008 for the Dow and Nasdaq, Mnuchin said in a tweet that he'd spoken to the CEOs of six major banks to ensure they had ample liquidity. Market participants, however, worried that Mnuchin's outreach effort may have created concerns about liquidity that had not existed prior to his tweet.