There is a plausible counterfactual argument for saying that, had he resigned with his old ally Robin Cook over the Iraq War in 2003, as his former admirers on the left would have expected him to, he could conceivably have mounted a successful challenge to Gordon Brown in 2007, standing as an experienced former minister on an anti-war ticket.
But it is clear that at some point around that time, Hain lost his balls. He failed to speak out against a war he must in his heart of hearts have opposed, and gradually, his left-field contributions to government policy-making dried up.
Never having been entirely trusted by the right and with his credibility on the left now badly compromised, it did not surprise me in the least that he performed so poorly in last year's deputy leadership election, when he found his whole USP had been successfully purloined by Jon Cruddas.
For me, that is what is so tragi-comic about Hain's current predicament - the fact that he spent £200,000 on a campaign which ended in near-humiliation for a man who once entertained serious aspirations to, if not the premiership, then certainly the Foreign Office.
Since then, he has gone on to win one small but important victory as Work and Pensions Secretary, overcoming Treasury objections to secure a £725m rescue package for 125,000 workers who lost pension rights when their employers went bust or wound up their schemes.
But even had the row over his campaign donations not occurred, I think it likely that he would have left the Cabinet at the next reshuffle, and hence I cannot help but think his time at the top of British politics is now drawing naturally to a close.
Who knows - if it meant Gordon could bring in Alan Milburn as Work and Pensions Secretary and stage a public rapprochement with the Blairites, then this is one crisis that the government might even be able to turn to its advantage.