I'm looking for an idiom or proverb that can be used for describing a situation in which someone's actions or behaviors are in favor of their opponents or enemies; in other words it seems that they are serving their enemies' or opponents' interests (usually unintentionally).
There is an Iranian proverb that says :
"To provide water for (turning) the enemy's mill"
This proverb mostly is used among politicians when they are accusing each other of giving advantages to the country's enemies, their opponents or the opposite parties.
It is supposed that a public election be held for choosing the members of the parliament on 26 February in Iran. Regarding the importance of this election, the supreme leader of the country has asked the politicians to stop using discouraging words or showing reactions that would lead people not to participate in the election. Because if the election is not recieved well by the people, it would be considered as a sign of their dissatisfaction from the current leaders and thus "would provide water for the country's enemies' mill".
What do English speakers use in this situation that can convey the same meaning?
I have come across this title " loading the gun of the enemy" in a website, but couldn't find it as a set phrase in available dictionaries.