But above all it is Trump’s authoritarianism that makes him unfit for the presidency — his stated admiration for Putin and the Chinese Politburo, his promise to use the power of the presidency against private enterprises, the casual threats he and his surrogates toss off against party donors, military officers, the press, the speaker of the House, and more.

All presidents are tempted by the powers of the office, and congressional abdication has only increased that temptation’s pull. President Obama’s power grabs are part of a bipartisan pattern of Caesarism, one that will likely continue apace under Hillary Clinton.

But far more than Obama or Hillary or George W. Bush, Trump is actively campaigning as a Caesarist, making his contempt for constitutional norms and political niceties a selling point. And given his mix of proud ignorance and immense self-regard, there is no reason to believe that any of this is just an act.

Trump would not be an American Mussolini; even our sclerotic institutions would resist him more effectively than that. But he could test them as no modern president has tested them before — and with them, the health of our economy, the civil peace of our society and the stability of an increasingly perilous world.