It takes a truly spectacular level of incompetence for an opposition leader to allow himself to be labelled soft on anti-Semitism.
What else can explain why it took Jeremy Corbyn no fewer than three attempts at issuing a statement of regret after it emerged that he had apparently supported an artist responsible for a grossly offensive anti-Semitic piece of public wall art in the East End of London?
Why else would he reply, when asked in a Jewish News interview whether he plans to visit Israel, 'At some point, yes, I will be in the Middle East,' so that it looked as if he was desperate not even to allow the word 'Israel' to pass his lips.
As it happens, I do not believe that Mr Corbyn is an anti-Semite. By which I mean that I don't believe he has an irrational hatred of Jews and all things Jewish. However, by his words and his actions (or, more often, his inactions), he has shown that he shares a mind-set that uncomfortably overlaps with those who really are anti-Semites.
In Mr Corbyn's case -- and in this, he is by no means alone, especially among those on the Left -- the thinking goes like this.
Israel is a major force of instability in the Middle East due to its fifty-year illegal occupation of Palestinian territory and its continuing oppression of the Palestinian people.
Israel was established due to the spread of a political ideology called Zionism, a racist creed that argues that Jews have more right than non-Jews to the land which they seized by force.
The vast majority of Jews are Zionists, and therefore, by implication, supporters of a racist ideology.
Conversely, anyone who supports the Palestinians must be an anti-racist, and therefore deserves to be supported, however much offensive nonsense they might spout about global Jewish conspiracies, the 'myth' of the Nazi holocaust, and how Mossad was responsible for 9/11.
Any self-respecting anti-racist must also, therefore, be an anti-Zionist. QED. (Why else, when he insists that he has always opposed anti-Semitism, does Mr Corbyn also insist that he has always opposed racism?) Correctly, he argues that anti-Zionism and anti-Semitism are not the same thing. Foolishly, he leaves himself wide open to criticism by consistently failing to make clear what the difference is.
Time and again, Mr Corbyn has found himself -- inadvertently, he insists -- in close proximity to the most obnoxious anti-Semites. He supported the East End wall artist without, he says, looking closely enough at his work. He belongs to closed Facebook groups on which all kinds of anti-Semitic garbage is spewed out because he doesn't have time to constantly monitor what is said there. It suggests a terrifying lack of concentration in a man who could soon be prime minister.
Time and again, those who swear allegiance to his cause slip across that line which they seem to have such trouble identifying. Christine Shawcroft, a leading member of Corbyn-supporting Momentum, and former chair of Labour's internal disputes panel, opposed the suspension of a local council candidate in Peterborough after he was accused of sharing on Facebook a piece of nonsense headlined 'International Red Cross report confirms the Holocaust of 6m Jews is a hoax.'
At Mr Corbyn's insistence, she has now resigned, although, bizarrely, it seems he's perfectly happy for her to remain a member of the party's national executive committee until the next NEC elections in June. As recently as last weekend, however -- yes, last weekend, not some time in the dim and distant past when no one seemed to bother about such things -- she apparently saw no reason why someone who shares Holocaust-denying drivel online should not stand for election under the Labour banner. Her excuse? 'I sent this email [supporting the candidate] before being aware of the full information about this case and I had not been shown the image of his abhorrent Facebook post.'
Well, excuse me if I don't buy it. Until this whole issue blew up in Labour's face, anti-Semitism among some of its members was so unremarkable that it routinely passed without comment. As recently as last Wednesday, a comment on a Facebook page called We Support Jeremy Corbyn referred to what it called 'the full onslaught of a very powerful special interest group [which] can employ the full might of the BBC to make sure its voice is heard very loudly and clearly.'
No prizes for guessing who the writer had in mind. Still, one anti-Semitic comment can hardly be evidence of a deep-seated problem, can it? Perhaps not, unless, as in this particular case, it was quickly approved by more than two thousand people, most if not all of them, presumably, supporters of Mr Corbyn.
The Labour leader insists repeatedly that not only is he a long-time campaigner against anti-Semitism but that he will not tolerate it in the party that he leads. I can't help wondering, however, why so many of his supporters seem not to believe that he really means it. Do they know something that the rest of us don't?
Perhaps they remember what he said in 2016, when he called an article by Jonathan Freedland of The Guardian, 'utterly disgusting, subliminal nastiness,' for having suggested that 'under Jeremy Corbyn the party has attracted many activists with views hostile to Jews.'
Which isn't quite the line he took this week in his letter to Jewish community leaders: 'I recognise that anti-Semitism has surfaced within the Labour party ... I acknowledge that anti-Semitic attitudes have surfaced more often in our ranks in recent years ...'
So which is it, Mr Corbyn? For a man of supposedly rock-solid principles, you are proving remarkably flexible. Or perhaps you're just slow on the uptake. Either way, it's utterly shameful.
Labour MPs who backed this week's Westminster protest against anti-Semitism are now being engulfed by torrents of threats and abuse. If Mr Corbyn wants to lead a party that embraces a kinder and gentler form of politics, the message is definitely not getting through to his supporters.
Why not? Because they know what he really thinks. They ignore what he says under pressure from the 'Murdoch press' and the 'Tory BBC'; they prefer to believe what they read on those closed Facebook pages that he supports: that the Holocaust was a hoax, the six million didn't die, and the world is run by a secret cabal of wealthy Jewish bankers.
And in case you were wondering: I am the son of refugees from Nazi Germany; my grandmother was murdered by a Nazi death squad in 1941; and I am not a Zionist.