I am an unapologetic, card-carrying liberal, and have been for most of my adult life. But I also try to be as open-minded as possible. I think of myself as a reasonable person, and I try to listen carefully to opposing points of view. On any political issue, if facts are presented that lead me to change my views, I am unafraid to make that change. There are issues that are very important to many liberals that aren’t important to me, and many issues that liberals favor and conservatives oppose where I believe conservatives are right. When that happens, I say so. I could give some specific examples, if you like. One is free trade, which I favor. I think it reduces poverty world-wide. Another is the Keystone pipeline, which I likewise favor.

The same is true of political candidates. I generally support Democratic candidates and oppose Republicans. But I have voted for Republicans in the past, and will probably will do so in the future. What I reject is the notion that Republicans, or any political opponents, are dreadful people. I thought the last two Republican candidates for President, John McCain and Mitt Romney, were decent, honorable and intelligent men. I thought they were both proven patriots. In both cases, I voted for Barack Obama, because generally I agreed with him on important matters of policy, and because I disagreed with Senator McCain and Mitt Romney on matters of policy. But that’s all. We just disagreed, and if they had won, they may well have turned out to be good Presidents. Just not as good as Obama.

George W. Bush was, I thought, a particularly poor President. But it’s not difficult for me to find important issues where he was right, and where I agreed with him, and thought he did well. He did a tremendous amount of good, for example, in combatting AIDS in Africa. PEPFAR, the President’s Emergency Plan for AIDS Relief, was a spectacular success, saving millions of lives. I think that Bush’s legacy is generally a weak one, that his tax cuts were ruinous and the war in Iraq grievously ill-considered. On balance, he wasn’t a very good President. But he also did genuine good in the world during his time in the White House.

Political campaigns are ugly things, with ferocious rhetoric on both sides. Partisans delight in making terrible personal attacks on their political foes. I deplore that. I wish we could all, liberals and conservatives, agree on this point: that both candidates are patriots, who just happen to disagree on matters of policy.

This is what I have believed and this is what I have written. This year is the exception. This year is genuinely different. For the first time in my lifetime, I am genuinely frightened for the future of my country. For the first time in my lifetime, we have a candidate for President who, if elected, seems to me to be genuinely dangerous. I consider myself a reasonable man. One candidate, however, defies reason, and requires an unreasonable response.

Donald Trump is the most dangerous candidate for President in American history. He cannot, and must not be elected. I do not say that, if he is elected, it will mean the end of the United States, that he is a danger to democracy. I don’t know that. But I do believe that he might pose precisely such a threat. And I don’t think that’s a chance we should take.

He has allied himself with dangerous forces of ethnic nationalism. I don’t particularly care if Alt-Right is meant to be tongue-in-cheek. Their rhetoric, and his rhetoric, is dangerously extreme, and profoundly anti-democratic. On crucial matters of race and ethnicity, Trump represents the most atavistic, nativist, and extremist strains in American history and current American society.

His economic plans, as outlined in his speeches and on-line, would impoverish our nation, increase our international indebtedness, and would, in all likelihood, lead to trade wars with many, if not most, of our leading trade partners–China, Mexico, the EU, South Korea.

His immigration plans are vicious, uncompassionate, and completely unworkable. The mass deportations he describes would badly damage our economy, while destroying the lives of millions of people, and ruining their family relationships. And let’s be clear, there’s not going to be, and shouldn’t be, a wall. (I have friends who point out that there have been times in the past when Hillary Clinton has supported building a similar wall. That’s true. She was wrong too.)

His foreign policies, such as they are, are built on a foundation of utter ignorance and foolishness. He has no appreciation for the complexities of foreign diplomacy, and no understanding of the challenges faced by our allies and friends. Worst of all, he expresses and fosters the most extreme contempt for a peaceful major world religion, Islam.

Worst of all, though, is Trump’s embrace of authoritarianism, for his rejection of fundamental democratic processes. In his acceptance speech at the Republican National Convention, Trump repeatedly insisted that he and only he could solve intractable national problems, that he and only he could Make America Great Again. For a student of history, that’s a frightening notion.

And his personality is incompatible with political leadership. This campaign has been so topsy-turvy, it beggars the imagination. But there is one event that I absolutely cannot imagine happening. I cannot imagine Donald Trump graciously conceding defeat. That’s something every losing candidate has done in the history of our great nation. And it’s the one thing of which I believe Trump to be incapable.

Though, of course, I would love to be proven wrong.

For this candidate, and only for this candidate, I do not say ‘he’s a patriot with whom I disagree.’ I say that this candidate, and only this candidate may represent a threat to the idea of America, to American melting pot multiculturalism, to American republican democracy, to the values that find such perfect expression in the Declaration of Independence, the Preamble to the Constitution, and to the Bill of Rights.

In a recent speech, Trump said to African-American voters, ‘what do you have to lose?’ I would answer that there is a great deal that we stand to lose. We cannot, cannot take that chance. Donald Trump cannot become President of the United States. Whatever we can do, consistent with our democratic traditions, we must do. I’m writing a check to the Clinton campaign today. I hope you will join me.