Leahy was elected to the Senate in 1974, making him one of its most veteran members. Backing Obama, then, is a subtle rebuttal to Hillary Clinton's frequent claim that her experience in the Senate and as first lady makes her more qualified to be president. If an old hand like Leahy thinks Obama is the better candidate, it might convince other elected Democrats and donors that the Illinois senator deserves their support.
Leahy also chairs the Senate Judiciary Committee and last year led the party's fight with former Attorney General Alberto Gonzales over the firings of several U.S. attorneys. His tussles with the Bush administration over Gonzales and other issues – especially civil liberties and other constitutional concerns – have made him popular with activist Democrats. Exit polls out of New Hampshire showed that Clinton beat Obama among registered Democrats, and the timing of this endorsement suggests it could be part of a bid to burnish Obama's credentials among that group.
Finally, Leahy has been an outspoken opponent of the Iraq war, and voted against the resolution authorizing the use of military force there – a resolution Clinton supported. Lately, however, the Clinton campaign, especially former President Bill Clinton, has been questioning the authenticity of Obama's opposition to the conflict. The endorsement from a consistent opponent of the war is a quiet rebuttal to the Clintons' assertions, and Obama alluded to the issue in a press release announcing Leahy's support.
"Senator Leahy had the judgment and courage to vote against the Iraq war, and he's been a champion of our rights here at home, and of human rights around the world," Obama said. "I look forward to working with him to stand up to the special interests, rally Democrats and Republicans together to get things done, and bring about change we can believe in."
Again, this endorsement, in and of itself, is unlikely to change any votes in Nevada and South Carolina. But it does indicate that the Obama campaign may be focusing on getting the backing of more Democrats to complement the candidate's existing edge among independent voters.