"to be caught in the undertow" can be used either literally or figuratively.
The literal meaning for swimmers is to be caught in a strong subsurface flow of water returning seaward from the shore as a result of wave action.
The figurative (idiomatic) meaning is to be carried in the opposite direction by popular opinion. Example: "He did not believe that global warming was being caused by human activity but he was caught in the undertow of political correctness."
- For Teachers