I wish this article were more clear as to whether these 27 reports pertained just to the USMC, or to all the armed services. Also, I didn't notice whether any of those 27 reports were proven false/unfounded.
Anyway, taking the "worst" - from the POV of the Corps - possible interpretation, that it was USMC only and all reports were true:
* In 5 years, 27 Marines were found to have been involved in "extremist activity"; just over 5 a year
* In 5 years, 27 out of ~182,000 Marines were found to have been involved in "extremist activity"; less than .02% of the Corps, if my quick very mental Math is correct.
I suspect that is a better rate than could be claimed for almost any US city of significant size. Ellison, Omar, and Tlaib will have a very difficult time inflating and pretzellating this into a claim that the USMC is a nest of combat-trained Neo-Nazis. Though I do expect them to try.