Hillary Clinton called Thursday for sweeping changes to elections and voting laws, arguing that measures including universal voter registration and national early voting are necessary to counteract a tide of laws aimed at making it more difficult for some people to vote.

Speaking at Houston's Texas State University, at a ceremony honoring the late civil rights leader and Democratic Representative Barbara Jordan, Clinton set her sights squarely on some of her potential Republican opponents, who she said are "systematically and deliberately trying to stop millions of American citizens from voting."

In one of her most powerful and passionate appearances of her campaign thus far, the former secretary of state singled out four current and former governors, whose actions "have undercut [the] fundamental American principle" of the right to vote in their "crusade against voting rights."

Instead of continuing along the same path, she said, "they should stop fear-mongering about a phantom epidemic of election fraud" and work to make it easier for Americans who want to vote to go to the polls.

All U.S. citizens should be automatically registered to vote when they turn 18 unless they take active steps to opt out, Clinton said, and all 50 states should allow at least 20 days of early voting. She also said she hopes to see Congress take action to roll back the Supreme Court's 2013 ruling allowing nine southern states to change their voting laws without federal approval.

"We need a Supreme Court that cares more about the right to vote of a person than the right to buy an election of a corporation," she said in an aside referencing that decision and her opposition to the high court's rulings that have allowed unlimited and undisclosed money to pour into politics.

Clinton's proposals are in line with what many national Democrats support, but are in stark contrast with the GOP, especially some of the men running for that party's presidential nomination. Since launching her campaign nearly two months ago, Clinton has shied away from directly naming those candidates, but on Thursday, she went right at them.

The first governor she mentioned, former Texas Governor Rick Perry, who launched his presidential campaign earlier in the day across the state in Dallas, described as "outdated and unnecessary" parts of the Voting Rights Act that were rolled back by the Supreme Court in 2013, she said.

She also took a swing at the Lone Star State's voter identification laws, saying: "You can use a concealed weapon permit as a valid form of identification but a valid student ID isn’t good enough."

In Wisconsin, Clinton said, Governor Scott Walker "cut back early voting and signed legislation that would make it harder for college students to vote," while New Jersey Governor Chris Christie refused to expand early voting. When Jeb Bush was governor of Florida, Clinton added, the state conducted "a deeply flawed purge" of voter records.

The Republican National Committee struck back, describing Clinton's rhetoric as "misleading and divisive," especially since her home state of New York does not allow early voting even as some states led by Republican governors do. "Her exploitation of this issue only underscores why voters find her dishonest and untrustworthy," said Orlando Watson, the RNC's communications director for black media.

While New York does not have early voting, Clinton during her time in the Senate supported versions of the Count Every Vote Act which, among other measures, would have required every state to offer early voting.

A spokeswoman for Maryland Governor Martin O'Malley, a Democrat, said that unlike Clinton, he "doesn't just talk about voting rights, he's shown the leadership to expand them," signing laws allowing early voting and online voter registration.

In 2012, just over 30 percent of votes in the presidential election were cast early. By 2012, it rose to 35 percent, as more states enacted early voting laws.

Clinton's call for universal voter registration follows the March signing of a bill in Oregon that automatically registers every adult citizen who has interacted with the Department of Motor Vehicles since 2013. The measure is expected to add 300,000 voters to the rolls. In 2009, then-Minnesota Governor Tim Pawlenty vetoed a bill that would have enacted automatic registration there, arguing that "registering to vote should be a voluntary, intentional act."

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