Trump needs to read up on history.
Are you sure he hasn't? Seeing that the NYTimes in 1903, Scientific American in 1904, and Pershing in his unfinished autobiography, notes for which are preserved in the Library of Congress and, thus, accessible to the public, all reported burying Muslims in a grave with a pig as an effective tactic against the Moro uprising, maybe it's Politifact, the latter-day NYTimes, and Snopes who need to read history -- from primary sources, not Howard Zinn and his ilk.
Trump himself didn't specify anything about dipping bullets in pig's blood, just advocated reading up on Pershing's counter-insurgency.