Now that the presidential race is truly on, anyone who cares about America's foreign policy and national security has no option but to vote for Hillary Clinton.
The most urgent reason is the need to prevent a mercurial, ill-informed hothead from ever having his hand on the nuclear button. The second reason is that Clinton has a particular skill set that suits these unstable times.
Donald Trump has shown over and over that he doesn't have the temperament to be commander-in-chief. He flies off the handle at criticism and shoots off his mouth with reckless abandon (like his call for Russia to hack and release Clinton's emails).
Many Trump supporters appear to believe he can compensate for his flaws by surrounding himself with foreign-policy heavy hitters. But he's failed to do so. Whereas Ronald Reagan, to whom Trump compares himself, had a vast array of foreign-policy advisers and a clear ideology when he ran for president, Trump has neither.
Trump has already terrified America's allies and thrilled our adversaries with his talk of dismantling our key alliances with NATO, Japan, and South Korea, and his praise for authoritarian leaders in Russia and China. He has suggested ditching an array of treaties that would undercut important international institutions.
Former Defense Secretary Leon Panetta, speaking last week at the Perry World House at the University of Pennsylvania, tried to imagine the situation if Trump were elected, and could hardly get the words out. "To think that someone like Donald Trump could become president," Panetta said, "and could back off our alliances, could say troops ought to torture, and that we ought to spread nuclear weapons and ban all Muslims - this is crazy.
"He has already jeopardized our national security, has already raised questions about where the United States is and will be."
Having recently returned from Germany and France, where I spoke with government officials and foreign-policy experts, I can attest to the bewilderment and shock of our close allies. "He can't possibly win, can he?" was the question I heard everywhere.
Our foreign partners are also bewildered at how eager Trump is to belittle them. After a French priest was murdered by ISIS - a tragedy that normally inspires condolences - Trump shot off: "France is no longer France." French President Francois Hollande angrily retorted: "France will always be France. It never gives up because it still bears ideals, values. . . . It's when you lower your standards that you are no longer what you are. That's something that may happen to others on the other side of the Atlantic."
Why insult an ally at such a painful moment? That question gets to the heart of why Trump presents such a danger to America's future. Trump appears to believe that America - and he, himself - can go it alone.
Which brings us to Clinton. No one can contest the breadth of her foreign experience, as first lady, senator, and secretary of state. She understands the critical need for the United States to maintain its role as a global leader at a time when Western democracies are in turmoil. She grasps - as Trump doesn't - that "Americanism" and "globalism" can't be separated. Prosperity at home requires stability abroad.
Moreover, Clinton recognizes that the global challenge to democracies from Moscow, Beijing, and ISIS requires that alliances be solidified, not broken.
Yes, she has made mistakes (who wouldn't have in decades of public service). Her staffing choices have not always been wise. Her use of a public email server was clearly unwise (although only a few dozen of 30,000 emails examined by the FBI had classified information). The Libya intervention ended poorly (although the options were all bad).
And the White House foreign-policy team left her little space to shape policy during her years as secretary of state. But what came through during her tenure was her toughness when confronting adversaries. In summer 2012, she - along with Panetta, CIA chief David Petraeus, and top military brass - wanted to arm moderate Syrian rebels (when they truly existed) as leverage to force Damascus to the bargaining table - which could have helped end the Syrian conflict. The Obama team refused.
Clinton has taken a firmer stand than Obama toward Russia's hybrid warfare in Ukraine. She has advocated a more forceful effort to end the ISIS caliphate (without sending U.S. ground troops). Yet her stance is far different from the reckless Trump rhetoric, which promises to defeat ISIS overnight but gives no details. As Clinton admitted at the Democratic convention, she is a stickler for details.
Of course, this is a bizarre election year - when the isolationist Trump has pulled GOP foreign policy to the left of Obama, and Democrats have taken on the mantle of patriotism. Clinton has the support of retired Gen. John Allen, and other retired brass, and clearly is comfortable dealing with the military. Yet some Americans may fear an activist Clinton foreign policy will pull the country into another conflict.
But Clinton has made clear that, whenever possible, she prefers tough diplomacy to force. She showed her chops when she maneuvered Europe, Russia, and China into supporting tough sanctions against Iran. The final Iran deal was negotiated after she left office, but she has pledged to hold Tehran to every detail.
Trump, on the other hand, wants to junk the deal, which would lead either to an Iranian nuke or another Mideast war.
Indeed, the irony of this election year is that the GOP, which was once the party dedicated to keeping America safe, has put forward a candidate whose temperament would gravely endanger U.S. security. That's why - whether or not you like Clinton - it's so essential that she be elected to the job.