Mitt Romney is also the only Republican to beat Hillary Clinton in a hypothetical matchup.
"Something is wrong with criminal justice in America," the senator wrote.
The Arizona Democrat is challenging the disqualification of 133 ballots.
Louisiana Dem says her GOP opponent voted to cut funding for schoolchildren to pay for it.
Warren will also visit the West Bank and Jordan in a move stoking 2016 speculation.
Finalists include Brooklyn, N.Y., Philadelphia and Columbus, Ohio.
Tea Party favorite drew applause from a crowd that included mega-donor Sheldon Adelson.
The potential '16 hopeful will keynote the University of South Carolina's winter graduation.
The Louisiana Democrat will take the field before Monday's Saints-Ravens game.
He retweeted at least a dozen tweets from random supporters urging him to run for president.