If something happens
all the way down the line, it happens at every stage of a situation or activity, or it includes all the people or things involved in a situation or activity.
The British government has fought for reform all the way down the line. Note: This expression has several variations. For example, you can also say that something happens
right down the line or
all along the line.
Republicans differed right down the line on what should be done. The survey shows support for the President's decision all along the line. Compare with
down the line.