First, let's clear up some misconceptions and clearly define agnosticism. There are varying degrees of agnosticism, which confuses the debate when used interchangeably. For instance, "strong agnostics" -- such as philosopher David Hume -- say the existence or nonexistence of God or the nature of ultimate reality is unknowable. "Atheistic agnostics" believe, based on logic, that God and the metaphysical world definitely do not exist.
But, it's not logical to say we can never truly know if there is a God, because as our scientific knowledge and investigative powers increase, our concepts of the universe constantly evolves. We discover new concepts that change our reality of the Universe: the lights in the sky are starts, the world is round, the theory of relativity, etc.
Scientists, theists and metaphysicians has all proposed various unproven theories of why we exist (in the spiritual, not physical sense) and what caused the beginning of the Universe (the "first mover"). But it's all conjecture and, as such, can simply be adapted to various political and social structures.
The best president would be one who believes in "weak agnosticism," which states that even though there is currently no evidence for the metaphysical or God, that does not mean evidence won't be discovered tomorrow. In other words, people can continue to be rationally justified in believing in the metaphysical until there is positive evidence to the contrary. Simply not having proof of the metaphysical or a "creator" is not enough empirical evidence to the contrary. An omnipotent God is unlikely, but we don't know for sure.
An agnostic president would respect all views, take them into account and than propose the best solutions. His/her values and beliefs are based in reality, logic, evidence and the present moment. Unlike theists that believe in some mysterious realm beyond time, physics and space.
Part of the mess in Iraq is due to Bush believing that this is a holy war pitting Muslim "fascism" (he uses the term incorrectly) versus Christian democracy. Instead of weighing the facts and expert advice about the situation, Bush went to war with God on his side against the "evil doer." The attacks of 9/11 and the response on both sides, have had as much to do about religion as oil.
More lives have been lost in religious wars than for any other reason in human history because religion can stir the soul to justify and rationalize heinous acts. Agnostics are less likely to go to war since they are ultimately pragmatic and usually resorting to violence is not pragmatic. Religious fundamentalism around the world would be met with cool reasoning.
An agnostic will take religion out of the equation, except when dealing with religious people and how their beliefs might affect various outcomes. Agnostics believe anything is possible and will respectfully acknowledge the religious beliefs of others, but will only act with evidence.
"So, you theorize that gay people are sinners and, thus, require punishment? That could be possible, but no one has proven it yet. Since it has not been proven, let's keep it in the very distant realm of possibility, but not act on that theory. Instead, let's continue with policies that assume gay people are simply an expression of biodiversity, requiring no unequal treatment. But, I will remember that you believe this since it affects the way you behave and communicate."
Political decisions are made with the common good in mind. In many ways, agnostics conduct their lives as humanists do: a person having a strong interest in or concern for human welfare, values, and dignity. He/she holds that people should think out questions of conduct for themselves. In addition to reason, agnostics also rely on emotion, feeling and desire and are usually very empathic to others.
Contrary to what religious folk say, agnostics are not nihilists or "wishy washy" in any way. Just because they are not bound by religious morals does not mean they "do whatever they please." They are concrete, scientific and rational. They are bound by "man's laws" and follow our innate social and biological axioms that help us to live in harmony (thou shall not kill, steal, etc.).
You don't need to believe in life after death or a higher purpose to cherish and value life. In fact, since Agnostics are truly rooted in the present and short of time, life if even more precious now. Agnostics are not marking time or blowing off mistakes by justifying that they can do better next time around or hoping for a "do over" to get to a good place in the afterlife.
Plus, since agnostics believe that anything is possible, there are always those nagging metaphysical possibilities at the back of their minds. We certainly could appear at the pearly gates after death...or return to this world as Paris Hilton's next Chihuahua...or this world could be another planet's hell... or we are all living in a giant computer generated animation... or life is just a big test in God college. We can speculate all we want and there are an infinite number of spiritual theories we humans can create.
Theists and atheists seem to have less respect for human life than agnostics. Not only do agnostics believe that there could be life after death, karma, retribution, etc. but they also believe this world, right now, might be all we have. This makes this life even more precious than for atheists, whose rationale for life is more materialistic. Agnostics have to walk a thin line: live for the moment but also for the future, just in case there is more.
Atheists cannot know for certain that the metaphysical does not exist. Do atheists really think they know that nothing will ever will be discovered beyond our current, physically knowable world? That's just as naive as theists blindly believing in Gods without any proof. While atheists might have a slight upper hand over theists since there is currently is no credible proof of a God or supernatural world, agnostics sit back and ask both groups: "Prove your belief!"
One thing we all know is that the universe and our very existence is extraordinary. The world filled with wondrous things still undiscovered. It seems to be important for our psychic health to explore these issues and take us beyond the mundane into the creative realm.
An agnostic president combines the best of both atheism and theism: they would recognize all the possibilities and empathize with the faithful, while at the same time focusing on the realities of human existence and acting for the common good. Unfortunately, it seems most dogmatic Americans are leery of the "unfaithful" and are not ready for an agnostic leader anytime in the near future.