What is the exact meaning of the phrase "could have stemmed from" in the following passage? The words in bold are intended:
The role of the Tudeh and its support of the Soviet Union's demand for an oil concession in the north or Iran were clear evidence of their closeness, especially when members of the party took to the streets in large numbers in favor of the Soviet bid. On balance, it could be argued that their support could have stemmed from a nationalist need to counter-balance Britain's predominance in Iran.
The ambiguous point is that their support was really stemmed from a nationalist need or not. Could have pp means that something was possible in the past, or you had the ability to do something in the past, but that you didn't do it. But a am not sure about this function in the above passage. I should say Tudeh was an Iranian communist party famous for supporting Russia.