What was the social, political setting that would allow Saul to hunt down followers of THE WAY and prosecute them in Jerusalem before the Sanhedrin?

Josephus tells us [Antiquities xi. 8,4-6] about the history surrounding Alexander the Great's conquest of Palestine. In this account it is recorded that the High Priest had been given a dream by God to meet Alexander outside the city gates with his priestly garments on and the priests behind him. Alexander was stunned and communicated that he had dreamed several nights prior, had seen this man (the High Priest), and was told that God, the God of this man (the High Priest) would hand the Persians into his hands.

Anyway, Alexander thus allowed the Jews to keep their Laws and continue to govern themselves. The Romans continued in this tradition, allowing Israel to self-govern. Of course they also had to pay tribute, or taxes.

The only thing the Jews had to guard against was the radical element in their midst, the far rightwing Zealots, that wanted to overthrow foreign rule so that Israel could be an independent nation again as they had been under King David. From around 200 BC to the time of Jesus was a period when apocalypticism was rife. The nation of Israel had an historical tradition of armies coming against Jerusalem: Antiochus in 168 BC erecting an altar to Zeus in the Temple; Pompey, who laid siege to Jerusalem in 63 BC; and again in 37 BC by Herod.

The Romans had very little patience for revolts, especially by people who wanted to do away with Roman rule. 1 Maccabees 15 (in the intertestamental literature known as "The Apocrypha") gives evidence that the Romans had granted the right of the ruling class in Jerusalem to apprehend dissidents and bring them back to the capital city for punishment. This appears to be what Saul is doing by traveling to surrounding cities/towns hunting down "the followers of The Way."

Rome apparently allowed the Jews to govern all Jewish people in Palestine even if they lived outside the borders of the nation of Israel: