President Obama was against Citizens United but had to use a super pac in 2012 to keep the contest close. Hillary Clinton is against Citizens United and has committed to only appoint SCOTUS justices who will vote to overturn this decision https://www.washingtonpost.com/news/post-politics/wp/2015/05/14/hillary-clintons-litmus-test-for-supreme-court-nominees-a-pledge-to-overturn-citizens-united/
Hillary Clinton told a group of her top fundraisers Thursday that if she is elected president, her nominees to the Supreme Court will have to share her belief that the court's 2010 Citizens United decision must be overturned, according to people who heard her remarks.
Clinton's emphatic opposition to the ruling, which allowed corporations and unions to spend unlimited sums on independent political activity, garnered the strongest applause of the afternoon from the more than 200 party financiers gathered in Brooklyn for a closed-door briefing from the Democratic candidate and her senior aides, according to some of those present.
"She got major applause when she said would not name anybody to the Supreme Court unless she has assurances that they would overturn" the decision, said one attendee, who, like others, requested anonymity to describe the private session.
If the make-up of the court does not change by 2017, four of the justices will be 78 years of age or older by the time the next president is inaugurated.
This is the only practical way to undo the damage done by Citizen United in that it will be impossible to get a constitutional amendment through congress and the states to undo this decision. That means that if you want to get rid of Citizens United, then one must support a candidate who can win in 2016 and support the most viable general election candidate.
Sanders would be a weak general election candidate and a defeat of the Democrats in 2016 will guarantee that Citizens United will remain the law of the land