By campaigning to get the legal drinking age changed, of course.
About a buck's worth of the better-known university presidents have decided to begin campaigning to get the drinking age lowered to 18. They claim that they only want to teach their students how to drink responsibly by offering the social situations that would allow it. They claim that they want to lower the instances of alcohol poisoning and binge drinking that occur among their students. They claim that they see it as a discriminatory policy, considering that these kids are old enough to vote, and to enlist, and to die, but are legally barred from drinking.
It's likely far from that altruistic.
Imagine being the university president, during whose tenure, underage drinking vanished on your campus. That's a pretty big feather in your cap, isn't it?
There are, of course, opponents. There are always opponents. Their side is mentioned in the news link above. I'll leave it up to you to decide which side you agree with.
Update: Here's someone's really amusing take on the situation.
17 minutes ago