Get/keep somebody onside phrase
To coax someone to back you up or to keep on backing you up.
John is the strongest in my school. If we can get him onside, we will win the fight.
Getting John onside boosts the morale of our team.
When the economy crashed, only a few companies were able to keep investors onside.
The verb "get/keep" must be conjugated according to its tense.
The origin of this phrase is not clear.
It was often said by a photographer when he would like small children to look at the camera and smile before he took a photo.
When the photographer said “watch the birdie”, all of us looked at the camera and smiled.