I bet Putin would be more afraid of Palin than Obama and Biden combined.
I bet Putin is equally unafraid of all of the above. In fact, considering the current U.S geopolitical position I think Putin will be quite content to stay in his backyard (sphere of influence) and watch things unfold. He knows all too well he doesn't need to get involved as we're working quite diligently to self-destruct our empire through over-extension, politically, economically and militarily. If anything, talking tough to Russia is the last thing anyone should be doing!
1) Economic troubles at home, not going away anytime soon
2) Massive commitments of manpower, material and money to eastern europian nations, the middleast, asia and certain south american countries.
3) Currently fighting two wars in Iraq and Afghanistan, yes troop reductions are coming in Iraq but there will always be a permanent presence of at least 20,000-30,000 in several major airbases, plus some of those troops will instead get shifted to Afghanistan, plus the army needs a breather to re-equip, re-train, repair etc.
4) Situation in Pakistan heating up. Pakistan has an army 600,000 strong and several division level commanders have issued orders stating that U.S forces crossing the border from Afghanistan are to be attacked as invading hostiles unless they knock and ask nicely to come into the country first. If new president of Pakistan can't control his folks it could turn into another shooting war with U.S forces involved.
5) Paraguay, Bolivia and Venezuela all very anti-US right now. Only major player in south America that's well and truly in the U.S camp and actively supporting is Columbia, which is also a big drain of U.S resources. Chavez has openly threatened to cut off Venezuela's oil imports to the States if things keep up this way, States currently imports more than 60% of energy from foreign sources. If this happens U.S will have to do something to try and stop Chavez, again requiring a lot of resources whether economic or military.
6) China's continually building up their military. They're still playing the waiting game but definitely aren't going to stay on the sidelines forever. Considering that they're in direct competition with U.S interests over resources in Africa and Asia, they'll most likely end up in the anti-U.S camp as well.