It is being said in many different ways in many different venues, but it is important enough to bear reiterating: Donald Trump can not be president. Like most public utterances, this one has several different subtexts and connotations, all of which are being vetted in various precincts of the blogosphere and punditocracy. I would like to speak to a very narrow range of this principle's meaning. I do not mean that Donald Trump can not be president in a moral sense, or a geostrategic sense, or by reference to the basic tenets of our system of government, though the assertion is true in all these ways (and others).
I mean that in the most practical, workaday sense of the phrase, Donald Trump can not be president. After his pronouncements in support of a ban on Muslims entering the U.S., there is no way that Trump could possibly perform the most basic functions of the office of president. No leader of a Muslim country (and few leaders of any other country that has a substantial Muslim minority, like France or the U.K.) could possibly engage in diplomacy with a Trump administration without suffering incalculable political damage at home. None of our alliances with nations like Turkey, Iraq, or Afghanistan could be maintained. U.S. military facilities in places like Turkmenistan might have to be closed. Trade pacts with Muslim nations would dissolve. The flow of commodities like oil might well stop. At the very least, the cost of doing business in the Muslim world would become subject to a "Trump surtax." All of these consequences flow immediately and spontaneously from Trump's pronouncements on a Muslim ban. It is a bell that can not be unrung. If he repudiates his comments tomorrow he will be no less hobbled in his potential for office.
This presents a conundrum to the Republican Party. If it nominates Trump, it is putting forward a candidate for president that is fundamentally unfit for office. Any candidate that upholds his or her pledge to support Trump if he is the nominee is either lying to the American people or is failing in a fundamental duty of citizenship. This is not partisan hysteria or liberal snark, it is a raw fact. Donald Trump can not be president of the United States. Anyone who denies this reality contributes to the political dysfunction that he embodies.