As the U.S. Supreme Court takes up the constitutionality of two same-sex marriage cases, including the federal "Defense of Marriage Act" (DOMA), U.S. Sen. Amy Klobuchar is circulating an online petition to repeal the law. The Minnesota Democrat is being joined in the Senate by New Hampshire Democrat Jeanne Shaheen. Both have signed on to DOMA repeal legislation. "This country was founded on equality for all people, and it is time to repeal this legislation both in Congress and in the courts," Klobuchar wrote in a email to supporters Monday. The effort comes a month after Minnesota voters defeated a constitutional amendment barring same-sex marriage, and as polls across the country show major shifts in opinion on same-sex marriage. The email serves as a reminder to gay rights activists, among them some who thought she was late to the cause of ending the military's "Don't Ask, Don't tell" policy. It also thrusts Klobuchar into a broader ideological debate, political turf on which she was less visible in her first term.