"Do we actually know who told Hillary she could use a private email? And has that person been drawn and quartered," longtime Clinton ally Neera Tanden wrote to campaign Chairman John Podesta in July 2015, just over five months before primary voting was to begin in the US states of Iowa and New Hampshire.
Tanden, who now serves on the Clinton transition team, is president of the Center for American Progress, a liberal think-tank that Podesta helped found in 2011.
Tanden was also concerned about a forthcoming CNN poll that she feared would show Sanders gaining on both Clinton and the Republican frontrunner at the time, former Florida Governor Jeb Bush.
"They [CNN] wouldn't tell me results, but if I had to guess it — discerning from our prep call — will show Bernie [Sanders] doing pretty well with Hillary and doing as well against Jeb [Bush] or close to it," Tanden wrote to Podesta.
At the time, Tanden was preparing for an appearance on CNN.
"Can you imagine what the Republicans would do to him [Sanders] if he were the nominee?" Podesta wrote in reply.
Tanden is frequently mentioned in the series of so called Podesta emails released by WikiLeaks this month.
Many of the emails involve strategy discussions as the campaign responded to multiple queries from the US Congress and the media over Clinton’s use of a private, unsecured server and email accounts during her tenure as secretary of state from 2009 until 2013, which is contrary US law and established prectice.