Bill McKibben, founder of the environmental group, speaks during the official kickoff to Senator Bernie Sanders' presidential campaign in Burlington, Vermont, U.S., on Tuesday, May 26, 2015. Shortly after declaring himself a presidential candidate, Sanders pledged to enact a Supreme Court litmus test if elected whereby he would not nominate judges who did not promise to overturn the Citizens United decision which ruled that the First Amendment to the Constitution prevented the government from restricting the amount of money that corporations and unions can spend on elections. Photographer: Scott Eisen/Bloomberg via Getty Images