I saw a t-shirt yesterday that had a picture of Dubs on it with the words “War criminal” under it. Yeah, funny but it got me thinking. Could the rest of the world legally hold a tribunal and convict (and sentence) an American official as a war criminal? Or do only we get to initiate these things because we have the biggest stick?
If the POTUS was so charged, who in this country would have the authority to give him/her up for trial?
When there has been no change in government, the only way this would happen would be for W to be captured by foreign forces and sprited away. Rather unlikely.
Define “legally”. Some countries have laws that would allow this, and some actual threats have been made to do it, although none I’d take seriously. We’ve debated this topic several times in GD, so if you do a little searching you might find some interesting threads.
There is certainly the precedent of trying a head of state as a war criminal: witness one Slobodan Milošević. But a country would have to be willing to face the wrath of the US in doing so-- no small deal. In any event, the US would not consider such a trial to be legal, as we are not signatories to the treaty establishing the International Criminal Court, and we withdrew from compulsory jurisdiction in the UN’s International Court of Justice in the 1980s.
Isn’t there a federal law requiring the President to invade the Netherlands if the ICC gets ahold of an American? 
I don’t know, but I’d be very surprised if there were. Besides, The Netherlands is part of NATO, and we’re required by treaty to defend them against attack, as are all the other NATO countries. We’d have to attack ourselves if we attacked them. 
This may be an Urban Legend, but I’ve heard that Henry Kissinger takes legal advice on which countries are “safe” for him to travel to, out of fear that he could be arrested a la Pinochet for his Vietnam War-era activities if he stepped into the wrong one.