By now, Labour's fate may well have been sealed. Many of those eligible to vote for its next leader will have cast their ballots soon after receiving them last week.
If the polls are right, and despite the continuing stream of allegations concerning his links to extremists, Holocaust deniers and antisemites, Jeremy Corbyn will be declared the winner on September 12. With that announcement, Labour's hope of avoiding a third consecutive general election defeat in 2020 will slip away.
But how, in the space of just under 10 years, will Labour have gone from having a prime minister who was prepared to put his job on the line to defend Israel's right to attack itself from Hizbollah terrorism in 2006, to being led by a man who campaigns alongside those who question the Jewish state's right to exist at all.
In retrospect, the first signs of this shift came in September 2010 when Ed Miliband delivered his first speech as Labour leader. Aside from Iraq, he discussed only one other foreign policy issue - Israel - and used it to deliver a call to lift the blockade of Gaza.
The words "Hamas" and "rockets" did not cross his lips. Thus did the new Labour leader casually cast aside the studded even-handedness of the Blair and Brown governments.
For the next four years, Mr Miliband continued in a similar vein: tolerating actions by frontbenchers - whether it was meetings with Hamas or joining boycott protests outside supermarkets - which would have led to dismissal under either of his two predecessors; showing little empathy for Israeli civilians under rocket attack last summer; and doing deals with virulently anti-Israel backbenchers ahead of last autumn's vote on Palestinian statehood.
At the same time, Labour's biggest paymaster - the Unite union - was undergoing a similar shift under its new leader, Len McCluskey. By last summer, it was depicting Israel as an "apartheid state" and "colonial oppressor".
With Mr Miliband's office "turning a blind eye", said one observer, Unite worked tirelessly to ensure its favoured candidates were selected in safe Labour seats.
After the general election, that contributed to a pronounced tilt to the left in the parliamentary party: MPs elected for the first time in May were disproportionately represented among those nominating Mr Corbyn.
Alone, however, these developments would not have left Mr Corbyn on the brink of victory; the hard-left MP only made it on to the ballot paper thanks to MPs - such as centrist London mayoral hopefuls David Lammy and Gareth Thomas - who made clear they had no intention of voting for him, and did not believe his candidacy would go anywhere.
Ironically, it was the outcome of Mr Miliband's desire - in the wake of revelations about alleged fixing by them of parliamentary selections - to show his independence from the unions that may turn out to be key to Mr Corbyn's election.
Changes to the party's rules for electing its leader reduced the influence of MPs and, despite warnings at the time of this danger, actually ended up boosting the influence of unions such as Unite.
Crucially, Mr Miliband's reforms have also allowed 120,000 non-members to register as supporters and vote.
This, said one insider, has developed into a form of "open source entryism", allowing hard-left activists from the likes of the Stop the War coalition and Palestinian Solidarity Campaign to vote for the man who has been a long-time champion of their causes.
But while very different from the narrow, secretive and ideologically rigid Militant entryism of the 1980s - which sent many previously Labour-voting Jews into the welcoming arms of Margaret Thatcher - it is likely to prove no less electorally devastating.
