Heritability Doesn't Mean Caused by Genes

It is possible to make genes more or less prone to mutation; even without evidence, we can assume Nature turns mutation up and down as convenient. E.g. sharks don't get cancer because the mutation settings are all at the minimum. E.g. the genes in the grass monkey brain actively reshuffle themselves even after genetic recombination, which is why IQ is 80% heritable instead of 100% heritable. 

There's also the height thing. Height is 80% heritable even though it's 100% genetic, because malnutrition or sleep deprivation can stunt you.

As a result (assuming you're not Judith Harris) heritability means both genes cause the trait and that the genes you use are a linear combination of the genes your parents are using. Even a quadratic combination puts heritability below 100%. (If you are Judith Harris you're either a fraud or incompetent. Sadly not limited to this one example.)

Political beliefs measure at around 30% heritable. This is almost certainly due to having the mutation setting on high, plus nonlinear effects from gene combination, plus nonlinear sensitivity to environment. You can safely predict someone's voting pattern by looking at their face for 5 seconds. It's biological and it's not subtle.
We can easily see that environment is a big factor; if you're predisposed to believe in communism but Karl Marx hasn't written his book yet, it's hard to believe in communism. George Orwell was predisposed to believe in "socialism" but his beliefs changed as a result of being exposed to socialism.
Changing your mind is also largely a genetic skill, which is an example of nonlinearity. Scientists measure beliefs by Scientist-assigned verbal category, not by subjective category, meaning the ability to change your mind based on evidence (possibly a relative 5% of the belief genome) can radically change your beliefs according to papers or studies.

We already know genes in the brain shuffle themselves a second time. This is because rolling the dice for high IQ is so valuable that it's worth the risk of getting snake eyes twice. Humans in particular are good at tolerating bad rolls due to being at the top of the food chain and having ecological dominance in general. Likewise the benefit for being a top human is huge. Grass monkeys are under strong upside selection pressure all the time. This is the reason dire apes are so prone to cancer.