John 1.19

'And this is the record of John, when the Jews sent priests and Levites and priests from Jerusalem to ask him, Who art thou?'

It is one of the peculiarities of the Gospels that the Jewish establishment  and their supporters are referred to as being 'the Jews'. Clearly John the Baptist was a Jew, as was John the Evangelist who wrote this particular Gospel. As indeed was Jesus of Nazareth, his mother Mary, his friends Martha and Mary, their brother Lazarus, and all the apostles too.
In the land of Israel, in those days, there were two hierarchical power structures, the military power and the ideological, priestly power. The military power was in the hands of the Romans and their collaborators, such as the Herods. The religious power remained with the Jews. So when the Evangelist states 'the Jews priests and Levites' he was referring to the indigenous religious elite, in the same way that we might say 'the Romans invaded Britain,' whereas most probably the majority of Romans had little to do with it.
The Roman government was not interested in John the Baptist because he did not appear to threaten them. On the other hand John was an increasingly powerful source of religious authority. They would want to assimilate or destroy.
Modern day Jews, like Reformed Christians, do not have priests and so both groups are a threat to the principle of earthly authority, and so both groups are often persecuted.
The 'Jews' sent the priests and the Levites to quiz John the Baptist because they felt threatened.