Labour has expelled Alastair Campbell, Tony Blair's former director of communications, after he admitted to voting Liberal Democrat in last week's European elections. Campbell, now a leading campaigner for a second referendum, intends to appeal the decision. He has characterised his vote as an attempt to "persuade Labour to do the right thing" on Brexit.

The news has been met with two sorts of reaction. The first is unsympathetic. Labour's rules expressly forbid members from supporting other political parties and candidates. Even allowing for the fact that Campbell revealed his vote on Sunday evening, well after polls had closed, his admission appears to be a straightforward breach of those rules. On those grounds, it is pretty difficult to argue with.

The opposing camp is nonetheless giving it a good go. They argue that Campbell has been made a scapegoat. Thousands of Labour members, they contend, are guilty of the same transgression -- not that they believe it to be a transgression at all. Bob Ainsworth and Fiona MacTaggart, both ministers under Blair and Brown, have revealed that they did not vote Labour 23 May either. "When you see a guy being expelled from the party for doing exactly the same as you've done," Ainsworth told BBC Coventry, "you stick your hands up and say, 'I am Spartacus'."

The charge made by Campbell and his supporters, then, is that the party is applying the letter of its rulebook rather too stringently. Or rather, that Jeremy Corbyn is seeking to impose standards to which he never bothered to adhere. The tweet the then MP for Islington North sent the morning after the Bradford West by-election of 2012 is getting a thorough airing, as it so often does at times like this. "Congratulations to George Galloway on astonishing result in Bradford," Corbyn wrote. "Big message here to opposition to wars and austerity." For this and other acts of insubordination, Campbell and friends argue, Corbyn was never expelled.

This leads us to the spirit in which those rules are applied. With news of Campbell's expulsion coming just over an hour after the Equality and Human Rights Commission launched its inquiry into Labour's handling of allegations of anti-Semitism within its ranks, his sympathisers could invoke an obvious -- and for the party leadership, unedifying -- comparison. Labour's processes for dealing with anti-Semitism have been widely criticised as sluggish, Byzantine, and opaque. Those MPs who sympathise both with that criticism and Campbell's position have drawn a contrast between the swiftness of his sanction and the often protracted routes taken to punishing members for anti-Semitism and other abusive behaviour -- or not. Campbell, they argue, has been summarily chucked for supporting a political position the leadership has since shifted to anyway. Jess Phillips puts it thus: "He was expelled quicker than a man who threatened to kill me, quicker than a man in my CLP who denied the Holocaust, both are only still suspended."

So who is right? Indeed, is there even a right? Let's consider the process first. It is not entirely accurate to say Campbell was expelled. Instead, his membership was terminated via a process known as auto-exclusion. The distinction is important: in the latter case, there is no disciplinary process, only a 14 day period in which the expelled member can provide evidence that they are not ineligible for membership. Campbell, who revealed his vote for the Liberal Democrats live on BBC News, might struggle there. Labour won't be drawn on who made the complaint that led to Campbell's auto-exclusion, but an online petition was circulated by grassroots members in the wake of his comments. It was always inevitable that supporters of the Corbyn project would pursue a bête noire of the Labour left in that way.

It's worth touching briefly on Corbyn's 2012 tweet here too. Plenty have argued that the two cases are comparable or equivalent. That argument is weak. Yes, both comments were made after polling had closed. But Corbyn, unlike Campbell, did not admit to voting Respect -- not that he could have registered to vote in Bradford West in any case. Nor did he encourage others to do so. Instead, he was making the same sort of political point that Labour Remainers have about the surge for the Liberal Democrats, Greens, SNP and Plaid Cymru. Politicians note the victories of their opponents, and encourage their party leaders to draw lessons from them, all the time. It doesn't follow that they endorse them over their own parties.

That holds true even for Corbyn's tweet. We can't know what he said or thought in private. You might make an educated guess, given his friendship with Galloway. But ultimately, we don't know. All we do know is that he toed the line in public. Our suspicions as to his inner sympathies don't matter. Take the case of Roy Jenkins. When his friend and disciple Dick Taverne quit as a Labour MP over Europe in 1972, he and many others agreed with his analysis of the situation but did not publicly endorse his independent candidacy in the ensuing Lincoln by-election. The warm words they offered in private are irrelevant to the question of whether they broke the letter of the rulebook.

None of that is to say, however, that applying the standard sanction -- or in these circumstances, not intervening to disapply it -- was a politically wise move. The Labour leadership is moving, albeit haphazardly, to reassure those Remainers who abandoned the party on 23 May that it has heard their concerns. Corbyn, for his part, is shifting on a second referendum. The hierarchy's deference to the remorseless logic of the rulebook risks creating the impression that they are building a cold house for the pro-Europeans it is professing to listen to. Indeed, it is wholly inconsistent with that entire (risky) gambit. Coming on the day that it did, it has also given those Remainers grounds to suspect that the party's approach to its rules is politically motivated. But it would be a category error to say these political questions were the same as the procedural one at the heart of the matter: did Campbell break the rules? The answer on that front is yes, until such time as the courts rule otherwise.