The landslide election of Jeremy Corbyn in September last year sparked sharp divisions within the Labour Party with senior figures distancing themselves from their new far-left leader.
There is no doubt he got off to a shaky start and has had to endure derision both in and out of Westminster for everything from his non-combative stance at prime minister's questions to his relaxed dress sense.
Indeed, there were predictions of an early leadership challenge and a shortlived tenure.
However, Mr Corbyn has ploughed on, quietly building his authority and pointing to a substantial increase in party membership.
He has also benefited from disarray in the Tory party which is tearing itself apart over Europe while ambitious figures are already positioning themselves as successors to David Cameron.
Of course, the real test for any leader is at the ballot box and Labour was looking towards local and devolved elections this coming week for signs that it was recovering from the drubbing it received at last year's Westminster poll.
But whatever plans and strategies the party had drawn up were completely blown off course by the extraordinary row over anti-Semitism which has erupted in recent days.
On Wednesday Labour MP Naz Shah was suspended pending investigation into controversial social media posts about Israel made before she was elected to Westminster.
If Mr Corbyn hoped the fuss over anti-Semitism in the party would then have died down, he was much mistaken.
On Thursday his close ally Ken Livingstone caused uproar when he defended Ms Shah's remarks, adding fuel to the fire by invoking Hitler saying: ``He was supporting Zionism - this is before he went mad and ended up killing six million Jews.''
He also claimed there was a ``well-orchestrated campaign'' against Labour by the ``Israel lobby.''
Mr Livingstone denies his remarks were anti-Semitic and remains unrepentant but his comments have caused deep anger.
Indeed, there were jaw-dropping scenes as a fellow Labour MP John Mann confronted Mr Livingstone in front of television cameras, accusing him of being a `Nazi apologist.'
After all this, Mr Corbyn had little choice but to suspend the former London mayor, who is no stranger to controversy.
In 2005, he compared a Jewish journalist to a `concentration camp guard' and when he refused to apologise was suspended for a month.
He has also been outspoken on Northern Ireland and once proclaimed that Britain's 800-year occupation of Ireland was more destructive than the Holocaust.
Mr Corbyn may be torn by loyalty to his old friend but this is a time when he has to show leadership.
This issue could prove absolutely toxic for Labour and he needs to act decisively to show that anti-Semitism has no place in the party he leads.
