(CNN) With the Iowa caucuses just days away, Joe Biden has turned to the simplest of arguments against the ascendant Bernie Sanders: He's not really a Democrat.

In the Hawkeye State on Thursday, Biden responded "I'm a Democrat" when asked the difference between himself and the Vermont senator. "Well, he says he's not," Biden added of Sanders. "He's not registered as a Democrat."

On Friday morning, in an interview on ABC's "Good Morning America," Biden kind of, sort of clarified those comments. "Bernie is a Democrat," Biden told George Stephanopoulos. "Bernie calls himself a Democratic Socialist. We have different views on a whole lot of things."

No, if you're asking, it is not an accident that Biden acknowledged Sanders was a Democrat only in the context of saying he calls himself a Democratic Socialist. And, if you're asking, welcome to politics!

Biden's last-minute attack on Sanders' Democratic bona fides echoes a line of argument that Hillary Clinton used to bash the Vermont senator during the 2016 primary fight -- and in her after-action report (in the form of memoir "What Happened?") of the race.

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