Interesting case law the above poster is referencing I think: https://en.wikipedia.org/wiki/South_Dakota_v._Dole
Notably one of the dissenting judges said this: "establishment of a minimum drinking age of 21 is not sufficiently related to interstate highway construction to justify so conditioning funds appropriated for that purpose."
It did however pass the supreme court at 7-2.
Not necessarily. Pretty much every state had to ask themselves the same question: "Do we care more about highway funding or the very small number of people 18-21 who vote?"
It's actually a very easy question in political calculus terms.
No.
Our political system involves some specific separations of powers, but politics is not fundamentally about thst.