This week, for the first time since moving to Israel 31 years ago, I registered to vote in an US election.This is a column to explain why. It is not though, an endorsement of any one candidate – though I freely confess that if I cast my ballot it will be for Hillary Clinton, in order to prevent the election of Donald Trump.Because more than once over the past decades I’ve written in these pages about my personal choice to no longer vote in the US, it’s worthwhile explaining why I think this time around is different.Why did I decide years ago to no longer exercise my privilege to participate in American elections? The answer is a simple thought exercise: Would I want a native-born Israeli who moved permanently to the US and became an American citizen with no thought of ever returning here, to continue voting in Israeli elections? To carry on influencing the course of government here, thus having a say in potential life-or-death policy decisions, for a country they no longer live in, or intend to live in? You bet I wouldn’t.So let’s be clear – this decision has nothing to do with my concern over the future of the US per se, or at least its domestic future. If a majority of Americans want to turn over their economy to a businessman who has more than once screwed over his partners and investors through multiple bankruptcies; it’s massive governmental apparatus to someone who has never done any form of public or military service; its legal system to a candidate who seems to have minimal knowledge of constitutional principles – well, that’s their poison to choose.Ah, so you’re thinking, this must be about Israel. Not at all. I’ve never been comfortable with the idea of a US voter casting their ballot primarily on the basis of whether a candidate would be “good” for Israel, depending on one’s interpretation of what that means.Voting in an American election should be decided upon the basis of which candidate will be better for the US, period. The American-Israeli relationship can be a component of that choice, but it surely shouldn’t be the decisive factor. If you think otherwise, I suggest you get on the next plane to Ben-Gurion Airport and join me here. To be honest, though, if confronted by a US presidential candidate who was either nakedly anti-Semitic or anti-Israel, I might find myself violating that principle and voting from Jerusalem based on strictly Jewish or Israeli concerns. But that’s never been the case in my lifetime, and it’s certainly not the case in this election.Hillary Clinton, whatever else she may be, is very much a classic center-left Democrat when it comes to Middle East policy, and there’s no reason to believe that once in the White House she will relate to Israel in any way significantly different than her husband did. That may mean some unpleasant moments for Benjamin Netanyahu in the years ahead, but nothing he can’t live with, which is why several members of his government have told me they’re entirely comfortable with the prospect of another Clinton presidency.As for Trump, I honestly have no idea what he really thinks about Israel, or if he’s even ever thought seriously about it at all. That’s why some of the most die-hard hardline supporters of Israel in the Republican camp – including Bill Kristol, Daniel Pipes, Eliot Cohen – have either declared their neutrality or support for Clinton in this race.Either way, Israel is today independently strong enough, and enjoys sufficiently broad support among the American people and political class, to survive just about any US presidential term of office, be it Clinton, Trump, etc.There’s no justification, in my view, to vote from in this election solely, or even primarily, over concern about Israel.So why vote now? Because along with being a citizen of Israel and the US, I am also, in a larger sense, a citizen of the world. And the US is the international community’s only democratic superpower, still the only reliable bulwark against the authoritarian forces that threaten the free world. The US president, constrained in many constitutional ways when it comes to exercising domestic political policy, has much broader power when it comes to foreign affairs, including the use of American military forces. That’s why the US president, for better or worse, is still the one figure who can be called the leader of the free world – and Donald Trump is, simply put, not fit to hold that position.I’m not going to go into the reasons for that; beyond the fact that they seem pretty evident to me, I’m not seeking to convince anyone else to follow my choice. I will say though, that as a native New Yorker of roughly the same generation, I’ve have the benefit of closely following Trump’s career and personal life as it was covered extensively by local media from its very beginnings; and there is nothing in that record to lead one to believe he is capable of responsibly holding down the fort in the White House, not for the US, or its allies.Of course, for some candidates, the heat of a presidential race is really their first significant political test, the first opportunity to prove their mettle and reveal something of their public character on a national stage. By this standard too, Trump has failed miserably. I don’t think Donald Trump is either stupid or a fascist, nor would I use those words to describe his supporters (though I would use deluded). He’s just a vain, shallow, irresponsible, emotionally unstable demagogue.The only comparable figure I can think of who has risen to the leadership of a modern democracy is Italy’s Silvio Berlusconi. But the US isn’t Italy, a country that seems to function in spite of its government, and one with little global impact.The final turning point in my realization that this time I needed to vote was the increasing body of evidence that Russian President Vladimir Putin is seeking to influence the election in Trump’s favor, and the Republican candidate’s apparent acquiescence to this move. Putin, while no Stalin, is still clearly the most dangerous global figure to emerge since the end of the Cold War, growing ever more brazen and reckless in his quest to restore Russia to superpower status.Trump’s dissing of NATO, his willingness to accept Russia’s moves into Ukraine, and the ties several of his closest advisers have to Putin or the oligarchs in his circle, is disturbing enough. His breezy dismissal of the Russian hacking into the Clinton campaign computer files made it absolutely clear Trump has no real idea of the potential threat an unchecked Putin would pose, and no inclination to counter it.Hillary Clinton, seasoned in foreign affairs and guided by experienced advisers, at least understands the enormousness of responsibility a US president takes on for the rest of the world. Donald Trump clearly doesn’t have a clue, and so must lose this election, preferably by a wide enough margin to definitively end his political ambitions.So that’s why I’ve preparing to vote in my first US election in over three decades. Of course, if Trump should for some reason drop out of this race, as some still hope he might, I’ll be more than happy to tear up my US ballot – and pray I’ll never have reason again to get another one.Calev Ben-David is the political/diplomatic correspondent for IBA English TV News. Comments welcome via Facebook/ Twitter.