Vance literally wrote the forward to an upcoming book by Heritage Foundation President Kevin D. Roberts, the organization responsible for Project 2025. It is absolutely relevant.
I associate and even am friends with all kinds of people I don't agree with. Implying that I endorse their views just because I associate with them would be to assign motivations to me that I don't have.
Writing an introduction to someone's book, as a public figure, is lending your reputation to them - that's the point, to put your name and reputation behind them, and so they can show that off for credibility.
