Demonstrators march in the snow outside the White House during a rally against the Supreme Court's decision five years ago in favor of Citizens United, which allows private citizens and corporations to make unlimited donations for political campaigns. Nicholas Kamm/AFP/Getty Images hide caption
Sen. Rand Paul, R-Ky., center, meets with members of the Londonderry Fish and Game Club in Litchfield, N.H., on Jan. 14. Paul was one of three GOP presidential hopefuls who attended Sunday's semiannual gathering of David and Charles Koch's donor network in California. Jim Cole/AP hide caption
Sen. Ted Cruz, R-Texas, leaves the stage after speaking at the Iowa Freedom Summit on Saturday in Des Moines, Iowa. Charlie Neibergall/AP hide caption
A demonstrator rallies outside the U.S. Chamber of Commerce against the Supreme Court's decision in favor of Citizens United five years ago. Eight protesters at the Supreme Court were arrested and charged. Nicholas Kamm/AFP/Getty Images hide caption
Former Florida Gov. Jeb Bush listens before a Nov. 20 speaking engagement in Washington. Susan Walsh/AP hide caption
Volunteers at the Lincoln Memorial help roll up a giant banner printed with the Preamble to the Constitution during an October 2010 demonstration against the Supreme Court's Citizens United ruling. Chip Somodevilla/Getty Images hide caption
The Supreme Court denied the petition of businessmen who say the 2010 Citizens United ruling makes it legal for corporations to contribute directly to candidates. The court building is seen here during renovations in December. Alex Wong/Getty Images hide caption
Voters participate in early voting Friday in Silver Spring, Md. Alex Wong/Getty Images hide caption
Costumed demonstrators on Oct. 3 in Denver, before the first presidential debate. Doug Pensinger/Getty Images hide caption
Sen. Jon Tester, D-Mont., faces a potentially tough re-election bid. Win McNamee/Getty Images hide caption