strengthen (one's) hand
To give someone the ability to do something better, more forcefully, or more effectively. The law aims to strengthen federal officers' hands when making arrests on suspicion of illegal immigration. The scandal is yet another issue that will strengthen her opponent's hand in the run up to the election.
strengthen someone's hand (or hands)
enable or encourage a person to act more vigorously or effectively.ˌstrengthen your ˈhand
give you more power to do something or act against somebody/something: The new anti-drug laws will strengthen the hand of the police.