Former Pennsylvania Gov. Robert Casey today became the first Democrat to threaten a 1996challenge to President Clinton. Casey, who just finished two terms as governor, established an exploratory committee to raise funds for a campaign. He is expected to decide whether to run by May. Casey, who opposes abortion rights, has complained that the Clinton Administration is filled with "left-wing ideologues." He had a heart and liver transplant in 1993. If he does run, he'll be running uphill.TIME Washington correspondent Michael Duffysays Clinton's approval rating among Democrats has dramatically improved this year, especially in early primary states, where Casey would have to start strong in order to mount a viable challenge.