He is essentially accusing our President - someone who has been leading our nation and allies in a long, bloody conflict against these terrorists - of literally being co-founder (with Hillary!) of the Islamic State (ISIL, Daesh, what have you).
Considering all of the things Trump has accused our President of doing - lacking any evidence to back his claims, and in fact going against all evidence we DO have - out and out Treason is a new low.
This is the standard attack plan of the con artist demagogue, since even before the days of Tailgunner Joe. Just accuse your opponent of anything and everything, including the aid and comfort of our nation's enemies, and never mind any consequence because you can claim First Amendment right as you campaign for public office. Never mind the outright lies, never mind the libel and defamation, never mind the distortion of history and reality. As long as your people eat it up, you'll keep serving it.
At some point, what Trump is doing is so obviously criminal that SOMEONE has to fucking arrest him for this. Force him to bring these charges to a grand jury, have him under oath, see him squirm then. Put him in jail for perjury, lying to a grand jury, lying to everybody. DO SOMETHING.
We should have ended all this crap back in the last century.