Of course he is. And he won't be satisfied with a recount, either, if he still loses. He'll claim it's voter fraud, Democrats letting non-citizens vote, hacking the voter machines, yadda yadda yadda.
Same thing will happen if Trump isn't re-elected in 2020. He will claim voter fraud, Dems cheated, Russia helped the Dems, etc etc etc. They'll have to send the military into the WH to forcibly remove him.