The problem with this story is it's been conflated with the Munich killings. Some want to claim he was commemorating a wreath for one of those terrorists, others are claiming he was laying a wreath for different people, and one of those terrorists had a monument in the vicinity of where he was.
He did write about his visit at the time, but he did NOT say he was laying a wreath for Black September member/s. He DID specifically say it was for others.
It's messy, maybe he shouldn't have done it, he wasn't the leader then, and maybe never expected to be, but that doesn't excuse him IF he's done something wrong.
But then we have to ask - what precisely has he done wrong?
And what if a politician doesn't believe the Israel solution is a solution? are they 'wrong' to hold that view? is it anti-semitic to side with a Palestinian view? Is it wrong to merely have sympathy for Palestine?
If I was a Brit in the 70's and 80's and sympathised with Ireland - I'd have faced a lot of backlash. Accused of being pro-IRA. Nowadays, that's less likely but back then...
I was too young then to have much of a view of the situation, but was anti-IRA because they seemed to be the terrorists (but I was ignorant of the opposing terrorism in NI).
If he's a supporter of Palestinians, I don't necessarily equate that with anti-Semitism, but I do know that if you're pro-Isreal, then anti-Semitism is precisely the accusation you'd lay at his door - because it's political dynamite.