Admittedly trust can be at times fragile, and can be lost almost instantly. This the normal kind of reaction to trust broken.
There is another kind of lost trust that comes intentionally. The intent is not with the two parties involved, but is an attempt by others to introduce doubt and distrust between individuals and groups. If the outsiders are successful, the previous relationship will implode and nothing will be the same. How can these attempt be combatted?
The parties who once trusted must communicate, so the exact nature of the distrust is pinpointed, and clarification obtained. If they can maintain enough trust to discover that the situation Is the result of outside interference, then the attempt fails. This is the way to close out the agitators and mute their devious ways.
We don’t have to be victims, we simply need to communicate. If there is adequate reason for mistrust, then so be it. It not, trust can be even stronger than before.