In a development that will be of intense concern to the 78-year-old Vermont senator and his supporters, it was reported that the so-called political action committee Big Tent Project Fund, had spent $868,000 on digital ads.

The group had previously spent almost $5m in adverts attacking the senator during the caucus in Nevada and the primary in South Carolina. Politico said the the nonprofit organisation — commonly known as a dark money group because it is not legally required to disclose its donors — said in a filing with the Federal Election Commission on Tuesday that it spent just the money in 10 states, all of which were voting today on Super Tuesday.