My suspicion on this - based on the 5 eyes context and our understanding of how the arrangement enabled all to spy on their own people by proxy - is that the partnership is also used to control elections in the same way.
The seemingly superfluous support/vote phrasing suggests that who you support and who you vote for may be different. How could I vote for a leftist? If my vote is intercepted and changed with help from one of the 4 foreign eyes.