The fourth perek of Massekhet Nidda is entitled Benot Kutim, and it begins by clarifying the status of Kutim – Samaritans – regarding the laws of ritual purity. Generally speaking, the Sages believed that the Kutim were scrupulous in keeping those mitzvot that they accepted. The Gemara explains that in the case of nidda, they declared a woman unclean after any bodily secretion, even after a green discharge, which does not render her a nidda. In the event that she subsequently menstruated, since the Kutim began her counting too early, they also concluded it before its time. This led the Sages to deem them ritually impure on a permanent basis.
During the following years there were continued tensions between the two communities, and Yoḥanan Hyrcanus led his troops into battle against the Samaritans and destroyed the temple that they had built on Har Gerizim. Nevertheless, there were also periods of cooperation, such as the period of the Bar Kokheva rebellion. As is clear in our Gemara, the attitude of the Sages towards them differed, although after a period of time a final conclusion was reached and they were ruled to be treated as non-Jews, due to their continued involvement with different types of idol worship.
It is important to note that the Gemara in Yevamot concludes that while a beit din should not accept potential converts whose reason for converting is anything other than a sincere desire to join the Jewish People, nevertheless, if such a person does undergo a full conversion process they are considered Jewish according to halakha. It is possible that the Kutim did not fall into that category because they continued with their idolatrous practices even at the moment of their conversion. Nevertheless, today, the community of Samaritans living in Israel are no longer idol worshipers, and there has been some level of acceptance of them into the larger Jewish community.