He keeps turning up at parties, sometimes with his terrible friends. You know when he walks through the door that there'll be trouble.

You've kicked him out but there he is, in the hallway, raucous and unbearable - his lowlife followers with painted faces and ridiculous Viking garb not far behind.

It's not that he gets drunk. After all, Donald Trump doesn't drink. It's just that the wannabe tyrant has no self-awareness, and his narcissism overrides all consideration for others. He is amoral and psychologically flawed.

You are well rid of him - except he hasn't got the message.

But do you ignore him, in the hope that he will drift away when Joe, your new partner, appears on the scene? Or do you confront him?

The Democrats, with a small number of Republicans, have decided to take him on by impeaching him.

Nobody blames them for their anger. There is little doubt that Mr Trump fired up a genuinely dangerous, armed mob.

Nancy Pelosi, the Democrats' leader in the House of Representatives, would have been lucky to escape with her life had the Trumpist crazies gotten hold of her. Some were captured in photographs carrying plastic zip-tie handcuffs.

On top of that, the riot at the Capitol was an outrageous assault on democracy which has appalled those few Republicans who see Mr Trump for what he is: an anti-democratic demagogue, stopped only (just) by the will of the voters.

But the problem with impeachment is that it is unlikely to work, and it may not be legal.

Impeachment is the formal laying of the accusation by the House of Representatives, and that's now been done.

The trial itself is conducted by senators, who have politics in the marrow of their bones. A guilty verdict demands a two-thirds majority of a Senate in which the Democrat majority is wafer thin.

Some Republicans may swing against Mr Trump, but probably not enough of them to convict. It is true that some have broken against the President - but not many. Mr Trump's supporters will determine their political futures.

"The President of the United States summoned this mob, assembled the mob, and lit the flame of this attack. Everything that followed was his doing," said GOP representative Liz Cheney. But Cheney, daughter of Dick, and Trump have fallen out before. There's history there.

Cheney's position, by the way, puts her somewhere to the left of Australia's acting Prime Minister, Michael McCormack, who was mealy-mouthed in his criticism: "It is unfortunate that we have seen the events at the Capitol Hill that we've seen in recent days, similar to those race riots that we saw around the country last year."

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Mr Trump will be out of office next Wednesday, and there is respectable legal opinion that a former president cannot be tried in the Senate.

"Once Trump's term ends on Jan. 20, Congress loses its constitutional authority to continue impeachment proceedings against him," writes J. Michael Luttig, a former appeal court judge, in The Washington Post.

Mr Biden is not keen on impeachment. It would overshadow his agenda right at the start of his term of office. It could dominated the whole of his tenure as he tries to remake the poisoned world of American politics, not to mention deal with the pandemic (and China and North Korea and Russia).

In a Senate trial, Mr Trump would present his defence, and who could doubt it would be a magnificent grandstanding of victimhood? It's what he is really good at. Television is the natural platform for his demagoguery.

And he would glory in his likely "acquittal", as he did when his previous impeachment failed. Two years ago he reveled in the failure to convict, waving the front page of the The Washington Post, with "acquitted" in a headline as broad as his grin.

Let the agencies of law enforcement go after Mr Trump if there is evidence of a crime. But keep the politics out of it.

If your ex behaves really badly, sometimes it's best to walk away with your new partner.