I'm verbose, but not eloquent.

I have several reasons for supporting Obama. Primary reasons include intellectual honesty, the embrace of community and individual ideals, the non-dogmatic willingness for dialogue and working towards a solution instead of believing that solutions are readily available and anointed by God...but also because I feel like we are witnessing a moment in history that signals the decline of the United States. The moment was not September 11, but September 12: The day the Bush Presidency was given the carte blanche. The beginning of the decline of pluralism, of a democratic morality, of national decency and integrity, and of the legitimacy of US leadership and influence.

Instead of trying to explain it myself, Andrew Sullivan (a very prominent conservative / libertarian) has put it much better.

But this much we can already say: Obama brings something no one else does to this moment. By replacing one of the most globally despised and domestically divisive presidents in American history with a young leader half-Kansan and half-Kenyan, America would be saying something to the world: Bush-Cheney is not who we are. America is not what it has come to appear to be. This country is among the most culturally and racially and religiously diverse on the planet. America has long been a powerful and vital beacon for human rights - not, as recently, the avatar of torture, rendition and executive tyranny. The simple existence of Obama as a new president in a new century would in itself enhance America's soft power immeasurably, just as a clear decision to leave Iraq would provide much greater leverage for diplomacy and military force in a whole variety of new ways. Obama would mean the rebranding of America, after a disastrous eight years....

This is the reason for his ascendancy. This is what the American people sense and the world awaits. This is what the Islamists fear. That last alone is reason to feel hope. Money quote [from Obama]:

We must [lead] not in the spirit of a patron, but the spirit of a partner – a partner that is mindful of its own imperfections. Extending an outstretched hand to these states must ultimately be more than just a matter of expedience or even charity. It must be about recognizing the inherent equality and worth of all people. And it’s about showing the world that America stands for something – that we can still lead...

[I]f the next President can restore the American people's trust – if they know that he or she is acting with their best interests at heart, with prudence and wisdom and some measure of humility – then I believe the American people will be ready to see America lead again.

They will be ready to show the world that we are not a country that ships prisoners in the dead of night to be tortured in far off countries. That we are not a country that runs prisons which lock people away without ever telling them why they are there or what they are charged with. That we are not a country which preaches compassion and justice to others while we allow bodies to float down the streets of a major American city.

That is not who we are.