At some stage during the Tribulation (first three and a half years), and before the Great Tribulation starts, the King of the North will start persecuting True Christians. Probably because they will be the only ones denouncing his true intentions whilst declaring peace and safety for all.
Daniel 7:25
He will defy the Most High and oppress the holy people of the Most High. He will try to change their sacred festivals and laws, and they will be placed under his control for a time, times, and half a time.
There will be some that choose to turn their back on God and be rewarded for their cowardness.
Daniel 11:30-32
But he will vent his anger against the people of the holy covenant and reward those who forsake the covenant. “His army will take over the Temple fortress, pollute the sanctuary, put a stop to the daily sacrifices, and set up the sacrilegious object that causes desecration. He will flatter and win over those who have violated the covenant. But the people who know their God will be strong and will resist him.
True Christians must expect to be tortured and killed during this time.
Daniel 11:33-35
“Wise leaders will give instruction to many, but these teachers will die by fire and sword, or they will be jailed and robbed. During these persecutions, little help will arrive, and many who join them will not be sincere. And some of the wise will fall victim to persecution. In this way, they will be refined and cleansed and made pure until the time of the end, for the appointed time is still to come.
After the Philadelphian Christians have fled to the Place of Safety, Satan now returns to persecute the True Christians that have chosen to remain.
Revelation 12:13
When the dragon realized that he had been thrown down to the earth, he pursued the woman who had given birth to the male child.