Sorry, but you need to know your history a bit better.. It was norm for men to swim naked, one of the reasons women were not allowed in health clubs etc, or if they were at only dedicated times.. Do a little research, you might learn something.
And as I said elsewhere this is a non issue, unless he was harassing them the fact he swam naked is not an issue. The Secret Services Job is to Protect, NOT to tell the person how to live, they are not there to behave how their bodyguards wish them to behave. If the female SS agents were uncomfortable guarding someone who likes to swim naked, that’s their issue, not his... and they should have requested transfer.
This is a non issue.
Your point, that bringing this up might make Joe Biden more sympathetic or might distract from other issues, is stupid.
Most normal people will think he at least has issues with judgment, or lack of consideration for others...at best. Many people, including me, will conclude he has sexual issues.
Sometimes, always being the contrarian just makes you wrong.