No one has worked more aggressively to trigger impeachment than the president. You may remember that, during the campaign, then-candidate Donald Trump suggested that, should he win, he might become one of the most “boring” presidents in history. There was in this curious pledge — which, as we now know, has been broken along with many other campaign promises — at least the slim possibility that Trump would recognize the crucial difference between running for office and running the country.

Imagine, if you will, the consequences if Trump had embraced this pivotal distinction. He need not have jettisoned many of his policy preferences. He could have still favored lower taxes, fewer regulations, tighter immigration controls, tougher trade policies against China and more pressure on our NATO allies to raise military spending. He might even have gently chided the Federal Reserve to loosen credit. Agree or disagree, these views are not wildly outside the political mainstream.

What mattered was tone — the ability to debate issues without impugning the character of his opponents. To be sure, partisan debate is full of exaggerations and simplicities. Still, it usually respects some bounds of truth and civility. Following this traditional path, Trump might have boosted his popularity, especially given the strong economy inherited from President Barack Obama. Even fierce critics might have conceded that, in practice, the “boring” Trump wasn’t so bad.

But that is not the path Trump chose. In many ways, President Trump has been more gratuitously offensive than candidate Trump. He is a proven liar, saying what he thinks his audiences want to hear. Glenn Kessler and The Post’s other Fact Checkers have counted more than 13,000 lies and deceptions.

Worse, Trump appeals to his supporters’ basest human instincts. He regularly uses immigration to stir racial and ethnic tensions.

He insults almost anyone who criticizes him. Trump fired Rex Tillerson, his first secretary of state, and later called him “dumb as a rock.” He has had four national security advisers, because he can’t hold advisers whom he ignores.

Most of his policies are collapsing. He has made no progress in limiting North Korea’s nuclear arsenal. His withdrawal from the nuclear arms agreement with Tehran seems to have emboldened the Iranians to a more violent role in the Middle East. Watching this, many Israelis wonder whether the United States would come to their aid if they were attacked by Iran or one of its proxies, according to news reports. His trade negotiations with China have fallen short, despite high tariffs imposed by both countries.

Now Trump has descended to new levels of recklessness with his behavior involving Ukraine and Syria. After consistently denying election “collusion” with Russia, Trump virtually begged the president of Ukraine to collude by investigating former vice president Joe Biden, a potential 2020 opponent. Trump’s abrupt withdrawal from Syria has shocked even many Republicans, who have deplored his decision as a strategic blunder and a moral outrage. We literally condemned to death many Kurds who had fought with Americans to defeat the Islamic State.

We face a terrible choice. Republicans argue that the rush to impeachment aims to overturn the 2016 election. True. They say this is bad for U.S. democracy. Also, true. One reason is legitimacy. What sustains successful democracies is the belief by winners and losers that they had a fair shot at winning. Faith in the system is more important than the result of one election. But if you start fiddling with the outcome — changing the result — you destroy this belief and put democracy at risk.

Because I respect this logic, I am an uneasy advocate for impeachment. If Americans don’t like their government, they can elect a new one. This is how mature and stable democracies are supposed to work. But there is at least one major exception: a situation in which the president’s behavior itself is so erratic and disconnected from underlying realities that it poses an immediate threat to the country. This is mostly a matter of judgment, but I conclude that Trump has landed us in this unfortunate spot. What might he do next?

The lesson of the Syrian debacle is that Trump is increasingly impervious to outside evidence and influence. No one knows what he will do, except that, reflecting his background as a reality-TV star, he aims to dominate the daily news cycle every day. This means he constantly needs new and more incendiary material. He incites his “base,” because he’s good at it and enjoys it. Inevitably, this dragged him toward impeachment.

According to the Constitution, the House first votes on the charges, which — if approved — would move to the Senate for trial, where a two-thirds majority would be required for conviction. It is widely assumed that few Republicans, if any, will support it, but events are moving so fast that this could change. I hope it does. Though scary, impeachment and removal are the lesser evils.