Greenwire: Sen. Arlen Specter’s party switch sent shockwaves across Washington yesterday, but it appears unlikely to significantly alter the prospects for President Obama’s agenda on energy, climate change and other major legislation. Certainly, Senate Democrats were visibly overjoyed with the prospect of holding the 60-vote majority that they have long coveted, as it should make it easier for the party to clear procedural hurdles. But top Democrats cautioned that they would still need to …