This is the kind of Chicken Little rhetoric that really bothers me. The world is not going to come to and end if Trump gets elected and neither will it end if Clinton gets elected. You got Clinton supporters predicting doom and gloom if Trump is elected and you have Trump supporters predicting doom and gloom if Clinton gets elected and it's all equally ridiculous. The US has elected far worse presidents than either of these candidates and both the US and the rest of the world were just fine and it will be the same now no matter who wins.
So while you all wring your hands over this election, I'm just going to sit back, relax, and enjoy my life. I'll be back in four to eight years to tell you all "I told you so" when the world is still completely fine after either the supposedly apocalyptic Trump or Clinton presidency.
As others have said, a president can do a lot of damage. Afghanistan and Iraq killed thousands of our troops, wounded and traumatized many more, killed who knows how many civilians, and (in Iraq) helped cause the creation of the Islamic State and all its atrocities. That's a LOT of suffering and death Bush caused.
Now, Trump is openly endangering the survival of NATO and the independence of the Baltic states with his threats to withdraw and his cozy relationship with Putin. Remember that Dean Acheson's comment about South Korea not being within the US defense perimeter helped give the Communist powers the impression that the South was up for grabs. Now Trump is doing the same thing with the Baltic. If the US withdraws from NATO, NATO will most assuredly collapse, and if that combines with appeasement from Germany and Putin's friends in FN, Putin will have a pretty free hand to, at the very least, force the Baltic states to agree to whatever he wants.
Trump is also not just permissive, but downright
enthusiastic about the chance to commit war crimes like torturing suspected terrorists with "a lot worse than waterboarding" and killing any family members of suspected terrorists. The man gets practically giddy at the thought of murder and torture!
On top of this, his election
will embolden racists, white supremacists, and hate groups in general. In fact, he already has. He has the endorsement of
the freaking KKK, for chrissakes, and David Duke has begun a bid for the Senate, citing Trump as his inspiration. The fierce nationalism behind the Leave campaign in Britain led to the murder of Jo Cox by a nationalist, and when Leave won anyway, harrassment of all kinds of immigrants, Muslims, and anyone who looked foreign skyrocketed. Harrassers usually made comments like "we voted to kick you people out!" Trump is more virulently bigoted, xenophobic, and permissive of violence against critics than Leave ever was, and this is in a country with a larger, more violent, and much more heavily armed society than Britain. If Trump and the
former head of the freaking KKK are openly running on a platform of bigotry and get away with it, and win, you can
guarantee that hate crimes and harrassment will become routine. Not since George C. Wallace has a presidential candidate so openly courted white supremacists. And this isn't even going into how Trump would encourage police brutality and a widening gap between rich and poor, which would assuredly cause increasing levels of poverty and crime.
Romney was nowhere near this dangerous. Nor was McCain. Trump is an egomaniacal, Russia-appeasing con artist with a decades-long streak of screwing over everyone he can get away with, and the American people and our international allies are not safe from this. He's so utterly ignorant of foreign and domestic policy that he wants to delegate both to advisors and the VP. He's hopelessly unqualified and even be knows it! And the trade wars he's eager to start would be devastating to the US and world economies. The Great Recession was bad enough, leading as it did to suffering across the world and the rise of right-wing parties with vague promises and bigotry.
So yes, it's fair to say that he represents an unprecedented threat to American and world stability, prosperity, and justice. Anyone who still is convinced otherwise by this point is sticking their head in the sand.