There is an experiment we can have the government carry out on many children and note and then correlate to those who choose in the future to openly support a political wing but it only can work if many are in the sample.
I strongly believe that adolescence masks true ideology and has a lot more delineation with one's true core system of ethics and social reasoning than childhood or adulthood do. I furthermore assert that those of us who seem to have changed our minds in life on politics had events and hormonal imbalance in teenage years that merely already pushed us away from the true wing we are.
What I am suggesting is that politics is far more nature than nurture but that nurture can force one who is built with one wing's psychology to vote the other only as a lesser evil and they will be anomalies in what I describe.
The sharing-justice duality test.
I want you to give a toddler/child the scenario where they believe that someone in on the experiment in front of them has stolen stealthily, bullied and finally convinced with words, another person (also in on it) to give them something that the child themselves values a lot and that the other seems visibly sad to have lost.
What is measured is the level of empathy, aggression, sadistic amusement, ambivalence etc that the subject displays towards the three situations.
It is important that the subjects are not having this done by or towards someone close to them, it must be strangers or people the child has barely met get (perhaps interacted with once first, to build some rapport, this will be fine-tuned).
Children who most fervently respond to the injustice in all three scenarios will be very passionate about politics as hey grow, regardless of wing. Those that truly are upset by all three scenarios, will be passionately left-wing, while those who are among the fervent that only reacted much when force was used, will be passionately right-wing. Those that are fervent with 2 scenarios but not in particular with one, will be centrists who grow cynical of the whole system.
Those that take sadistic amusement, least when the person is talked out of it, and giggle at the whole situation, will grow to become right-wing Libertarian or some corporatist variant (even as far as ancap but not necessarily).
Those that seem to not care much at all, will grow to not vote.
Those that display fear and try to escape the room or look down at the ground wishing they could help, will become social democrats AKA progressives of a less severe kind than the fervent types.
It will be discovered that any other possible reaction combination simply never happens. It will be important to do the talking part last, so that the child understands that the talk is based on guilt-trip manipulation and not just genuine care and share mentality. The children who react barely at all to the talking part but to the other two will be left-leaning centrists while other 2-1 combinations will fluctuate in life, as the cynics hypothesised.