There is a flight from the centre towards the far left and the far right.
Those involved in the flight to the left - Sanders and Corbyn supporters say - have to be aware that an equal and opposite movement to reactionary extremism is happening at the same time.
And that the two phenomena may not be disconnected. History certainly seems to suggest otherwise.
They can look back at the Spanish Civil War and think 'ooh I would have supported the Republic', but what they should be thinking is that the Spanish Civil War was something worth preventing at all costs.
Another example of the wood and trees bias problem flagged up below.
We need to temper our ideas and resulting actions with a sense of context.