Jeremy Corbyn claims to be a "straight-talking" politician. Yet there is one area in which he has been reluctant to give any straight answers since becoming Labour leader.
The question of whether he would ever support the UK taking military action is one which he has repeatedly dodged and fudged.
Asked during a Labour leadership hustings last night, whether he would defend a Nato ally invaded by the Russians, he replied instead that he would seek to avoid any such conflict happening in the first place.
"You would obviously try to avoid that happening in the first place, you would build up a good dialogue with Russia to ask them and support them in respecting borders."
Pushed on what he would do if the Russians failed to respect those borders, he replied:
"I don't wish to go to war. What I want to do is achieve a world where we don't need to go to war, where there is no need for it. That can be done.”
Of course we would all like a world in which there is never any war. However, while we await the coming utopia, the question of what a potential prime minister would do were such a war to actually take place still needs to be answered. For Corbyn to refuse to do so puts him in a position never before occupied by the leader of any major UK political party.
This vitally important question of whether he is a pacifist is one he seems strangely torn on.
Asked last November whether he was a pacifist, he told Andrew Marr that he "wouldn't describe myself" as one. He has also said that war should be "a last resort"
However, when asked the same question just months before when running for leader, he replied that "I'm not sure" whether he was a pacifist.
Asked by the Church Times last year whether he would have supported British people who joined the International Brigades during the Spanish Civil War, he replied:
"My dad wanted to join the International Brigade, but his health wouldn't allow it. Would I have supported it? You can't translate yourself into a different period; but had the rest of the world properly recognised and supported the Republican government in Spain, would the Second World War have happened? We'll never know. I do have respect for those people that were conscientious objectors in the war. Does that make me a pacifist? I can't really answer that. I'm not sure."
There was a similar reluctance to speak about this subject during a leadership hustings last year. Asked by rival candidate Liz Kendall whether there would be any circumstances under which he would support military action, he replied that there may be some but "I can't think of them at the moment."
Perhaps the simplest way to work out whether Corbyn is a pacifist is to find out whether there are any previous wars he has supported.
If you look through Corbyn's record, there are no previous examples of him supporting military action by the UK. He famously opposed the Falklands War in the 1980s and even now reportedly favours a power-sharing deal with the Argentinians.
During the last Labour government, Corbyn also opposed, not only Britain's involvement in Iraq and Afghanistan, but also our successful intervention in Kosovo. In 2004 he signed an early day motion attacking the "so-termed 'humanitarian' invasion of Kosovo."
Not only did Corbyn not support the Nato intervention in Kosovo, but he has also long opposed the very existence of the organisation. In 2014 he spoke at a "No to NATO - No New Wars" in which he called for Nato to "shut up shop, go home and go away".
With this in mind, his reluctance to answer the question of whether he would support a fellow Nato member under foreign invasion becomes easier to explain. Not only does he not want to defend our Nato allies, he doesn't even think we should be their Nato allies in the first place.
Of course the question of whether a prime minister Corbyn would ever sanction military action is not one that is ever likely to be tested. Corbyn and his party's current polling suggests the chances of him ever entering Downing Street are wafer thin.
However, as the leader of the UK's main opposition party there is at least a theoretical possibility that he will one day be in the position of deciding whether or not Britain should take military action to defend our neighbours and allies. All of the evidence we have suggests that he would almost certainly decide not to do so.
That is worrying, not just for Labour's electoral future, but for the very future security of Europe. It also places him in total opposition to the vast majority of his own parliamentary party. That may not sound like anything particularly new. However, until now, most Labour MP's criticism of Corbyn has focused on doubts about whether him becoming prime minister will ever be possible. After yesterday's comments, many of them will be asking instead whether it is even desirable.