The Obama administration didn't change the rules regarding a schools obligation to investigate harassment. Here's the original guidance letter:
https://www2.ed.gov/about/offices/list/ocr/letters/colleague...See footnotes 10 and 12, which lay out the precedent that sexual assault alone could create a hostile environment.
What apparently did change was that prior to the letter some schools applied a "clear & convincing" standard to adjudicating harassment complaints, while the letter demands (citing some precedent) that the proper standard is "preponderance of the evidence". See pp 10-11.
But I don't think that's the critical change. From what I can piece together, the Obama letter was basically a notice that regulators were going to put more effort into enforcing the existing law. This type of shift of emphasis is common. When that notice went out, colleges did as all large organizations do to show obeyance--they made a show of reviewing their procedures and requiring completion of more sexual harassment training by their personnel.
Coincidentally (or maybe not so coincidentally) there was some new "science" about the psychology of sexual assault that had begun to dominate the discourse. And one researcher in particular, Dr. Rebecca Campbell, gained widespread recognition and invitations to "educate" college administrators on matters of sexual assault. Dr. Campbell's ideas have since been roundly rebuked (if not completely rejected), but for a few years they figured heavily into how some colleges designed and applied their adjudication procedures. See https://www.theatlantic.com/education/archive/2017/09/the-ba... for the long story.
But for this bad "science" making the rounds, I think the Obama-era increased enforcement would have mostly gone unnoticed, save for marginal changes in the speed and resolution of sexual assault complaints.
EDIT: And there it is in this article: "But she also described with astonishment a training session she had attended in which the concept of 'trauma-informed investigation' was taught." That's the Dr. Campbell research, likely presented by Dr. Campbell herself.