According to the Washington Post, "During 11 hours of hearings on the September 2012 terrorist attacks in Benghazi, Libya," on 22 October 2015, "House Republicans" on the Select Committee on Benghazi "seemed singularly focused on one man — a man who has never held public office, a man who is not officially on the payroll of Hillary Clinton's presidential campaign and a man who has no official capacity to influence American foreign policy." The reference here is to Sidney Blumenthal, and "According to the Huffington Post's Sam Stein, in the first session alone [...] he was mentioned exactly as many times as the U.S. ambassador who died in the Benghazi attacks."
By the initial count of the more right-wing Washington Examiner, the Republicans on the Committee showed "a near-obsession with Blumenthal. His name was mentioned 60 times — before the first questioner had even finished."
I won't speculate on motivations, but the effect of the invocation of Blumenthal's name was that figurative dog-whistle for part of the base of the Republican electorate.
"Sidney ... Blumenthal": Insider, big-city boy (from Chicago), intellectual (Brandeis graduate, former journalist), friend of the Clintons, Jew. Another sign that control of the country is slipping out of the hands of "real Americans": God-fearing, small-town patriots dedicated to the USA as a (White, when I was growing up — and "White" in that formulation didn't always include Jews) Christian Nation.
So keep your ears cleaned out and listen up. As Clinton and far more so Bernie Sanders continue their runs for president, the whistling will get louder and more audible.