There’s a fun story in today’s Sun drawing on recently declassified Czech intelligence: that in 1986, a Czechoslovakian spy met with Jeremy Corbyn under diplomatic cover, but failed to get any high-level information of him, though Corbyn was considered to be of potential value enough that he was given the nickname “Cob”.

Czechoslovakia’s intelligence community doesn’t particularly come out of the story particularly well: all they gleaned from their meetings of Jeremy Corbyn was that he was critical of the United States and even more hostile to Margaret Thatcher’s government.

How much does this stuff matter, electorally speaking? From a Conservative perspective it confirms their belief that a Corbyn-led government would drag British foreign policy in a new and catastrophic direction, with potentially disastrous consequences for the future of Nato. (From the perspective of some longtime Corbynite loyalists, this is part of the point.)

As far as voters go however, the story is likely to fall flat, for three main reasons. The first is that foreign policy, particularly the foreign policy of the opposition, tends to be low-salience among all voters, regardless of age, income or class background, particularly when the economy is not doing so well. The second is that the past is even less important. People vote on the future.

But the third problem with this line, and indeed a lot of the anti-Corbyn messages that the Tories are using, is that they are simply counter-intuitive. We're hard-wired to enjoy being validated and to disregard things that challenge our strongly held opinions. (One of, but not the only, reason why the last general election was so volatile is because most voters actually didn't know Theresa May or Corbyn all that well, as strange as that may seem to people who follow politics regularly.) People don't believe that the United Kingdom could ever “become like Venezuela” because that is so far removed from their sense of the UK as a strong and resilient country, and the current orthodoxy that politicians can bring about meaningful change.

People also tend to switch off whenever a political attack gets too animated. The frothy tone of most anti-Corbyn messages is self-discrediting. As Tony Blair noted in his memoir, The Journey, the most effective attacks are often the smallest, because the leap people have to take is not that large. He didn’t attack William Hague as a sinister small-state politician, but instead described him as being better at telling jokes than making good judgements.This worked a lot better, not least because people already thought Hague was good at jokes, so it wasn't the world's biggest leap. Compare and contrast that with Gavin Williamson's response to today's story, which is to say that Corbyn “can’t be trusted”, a far bigger claim. At best it raises eyebrows, but most people just switch off when they hear that kind of talk from one politician about another.

Now, it is of course true that a Corbyn-led government would do foreign policy very differently than any previous Labour government. Perversely, the attack line that might work is actually a lot less fair: it’s to say that it shows that his judgement is suspect because he didn’t work out that he was meeting a spy. Of course, you can fairly point out that the point of being a spy is to avoid detection, but because people already think of the party he leads as the nice and soppy party, telling people that he was too nice and soppy to spot a spy and therefore too nice and soppy to be Prime Minister confirms part of what they already believe.