Since your son’s main interest is political policy work, I would think that there’s an enormous advantage to being in the state capitol. It’s where the HQ of the state parties would be and where there should be opportunities for internships.
A little googling reveals some articles on line about politics on each campus. In both cases, the campuses lean heavily to the left - almost to the exclusion of any competing ideas. This is a problem for someone who wants to study or be involved with political policy because the range of points of view is limited, debate is limited, and there seems to be a lot of pressure to adher to an orthodoxy. My brief search suggests that Mac has made more progress in wrestling with this than Carleton has. A more in depth s arch by your son would likely be an educational experience for him.
The advantage of being in the state capitol really emerges if you see the campus as a liberal bubble where there is no real debate and examination of contrasting ideas. (I say that as a liberal.) The only way to find that is to get off campus to some place like the state legislature to see ideas challenged and to get involved with politics in action.
Both of these are obviously excellent schools as you’ve mentioned. I know only one person from each and they’re both exceptional human beings. I don’t know if this is typical, but the friend from Carleton went into urban planning after college but then transitioned to organic farming after just a year or two. She and her husband, whom she met at Carleton, today own a successful organic farm which employs half a dozen interns each year. Gotta like the open mindedness and ability to put ideas into action of those Carleton alums.