Context for anyone who doesn't remember his February 19th, 2016 campaign speech:
They were having terrorism problems, just like we do. And he caught 50 terrorists who did tremendous damage and killed many people. And he took the 50 terrorists, and he took 50 men and he dipped 50 bullets in pigs’ blood — you heard that, right? He took 50 bullets, and he dipped them in pigs’ blood. And he had his men load his rifles, and he lined up the 50 people, and they shot 49 of those people. And the 50th person, he said: You go back to your people, and you tell them what happened. And for 25 years, there wasn’t a problem. Okay? Twenty-five years, there wasn’t a problem.
Of the many atrocities the Americans committed in the Philippines, pig bullets wasn't actually one of them (although mass execution of males over the age of 10 was), but pigs being Muslim kryptonite is a popular myth among the alt-right.