Eau Claire, Wisconsin(CNN) Hillary Clinton wants voters in Wisconsin to know that she has been a Democrat for much of her adult life. Why? Bernie Sanders hasn't been.
Clinton said her near-lifelong membership to the Democratic Party was "important" in the nomination contest while campaigning here on Saturday, two days ahead of Wisconsin's Democratic primary.
"I am also a Democrat and have been a proud Democrat all my adult life," Clinton said. "And I think that is kind of important if we are selecting someone to be the Democratic nominee of the Democratic Party."
Clinton grew up in a Republican household and was briefly a Republican when she went to Wellesley College in 1965. Shortly after arriving on campus, however, Clinton grew more liberal and has been a member of the Democratic Party since her graduation in 1969.
Sanders, however, has never been a member of the Democratic Party and is one of two independents in the United States Senate.
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Sanders has caucused with the Democratic Party ever since he came to Washington as a congressman in 1991. He unsuccessfully ran for the United States Senate in 1971 as a member of Liberty Union party and, in 1981, when he successfully ran for mayor of Burlington, Vermont, he did so as an independent. At times, the senator identifies as a democratic (small D) socialist.
Sanders, however, listed the Democratic Party as his party affiliation in his statement of candidacy for his presidential run. He also declared as a Democrat during the New Hampshire primary.
Sanders has also, at times, said he would never be a member of the Democratic Party.
"I am not a Democrat and have no intention of becoming one," Sanders wrote in a letter to an academic as mayor of Burlington in 1988.
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Sanders' party affiliation was a larger story earlier in the presidential campaign, when Democratic officials openly questioned whether Sanders would be able to win the nomination as someone who never registered as a Democrat.
Before he declared his run, even Sanders acknowledged it could be an issue.
"I am getting balder and balder trying to figure these things out," he said in February 2015. "That is a decision I would have to make."