You don't inherit it, it's part of your beliefs and choices, not your genes. "Inherited" is an invalid term, implying it is genetic or a physical object passed down. Many people change political parties and opinions. There have been instances in history in which political candidates have done so.
First of all, please note that I specifically made a note about the true unit of inheritance likely being attitudes towards specific ideas, not to party membership itself. Its just that over a few generations political parties tend to be reasonably consistent, so tendency to believe particular ideas -> tendency to belong to particular political parties. When you realize that political party ideology is a group of ideas, each of which is heritable at some frequency, you'd expect political party to be *more* heritable than any of its component ideas (because people who believe in some critical fraction of them are going to prefer that party to the competition), especially in a political system as bipolar as the US. That is, as long as there is philosophical continuity within the party.
These are also tendencies, not guarantees. Just like you can't perfectly predict your height based on your parents' heights. Statistically the heritability of political party is above .8 for the time period when the study was conducted (that is, better than 80% agreement between parents and their children, the time period being relevant because there was philosophical continuity within parties). This means that 20% of the time there won't be agreement.
Finally, you make claims but have no warrants to justify those claims. "You don't inherit it, it's part of your beliefs and choices, not your genes." Why? I've cited evidence to the contrary. Your saying things work in a way that doesn't conform to actual data isn't going to make me change my mind. If you want to debate this, you need to bring actual evidence to the table, not just baseless claims.
Also; Let me get this straight. You take every word of this Steven Plinker for fact just because he said in his book that he had evidence? Does he have a direct reliable source? What is this "blank slate" thing? That's vegetables and fetuses, dude. Why does it seem to imply that people's choices are genetic? No, people aren't blank slates, but they're written with chalk.
He didn't just say he had evidence. He cites a remarkable amount of primary literature and *describes the results* of those studies, sometimes in meticulous detail. I also don't think every word of the book is gospel truth - some of the chapters weren't as meticulous. But you are welcome to read his book for yourself and make your own assessment. I found the scientific data relevant to the conclusions i've referenced compelling.
I certainly find Pinker's book more compelling than your "no its not true" line of argumentation with only the meagerest anecdotal evidence in support.
The Blank Slate concept is the pure nurture side of the nature vs. nurture debate. Its also clearly wrong a priori. The part of our body that 'makes decisions' is the brain. Its a bio-chemical organ. It develops and operates based on blueprints found in our genes. The very idea that how the brain operates is going to be independent of genetics is both laughably naive and lacking in evidentiary support.
FWIW, other evidence from the primary literature:
The heritability of partisan attachmentMartin, NG, et al. Transmission of Social Attitudes. 1986. PNAS. 83(12): 4364-8. (not available online, sorry)
The heritability of attitudes: a study of twinsI'm sure if you are sufficiently motivated you can find additional literature.