If by all Federal Grants, you mean including Research Grants, than yes that along with suspension of other Federal Aid will be an eye opener. In FY2014 (Can’t find anything more recent), Harvard was awarded $609M in federal grants. It also submitted requests for an additional $2.8B in grants.
It's probably a good thing I'm not in Trumps position....If it was up to me id whittle that endowment down so that in a 100yrs when you Googled Harvard.....In would answer....Harvard Beets!.... http://allrecipes.com/recipe/92773/grandmas-harvard-beets/