Strenght of one vote in US Senate elections differs according to the state the person lives in. California and Wyoming both have two senators, but a number of voters differ, right? So the vote of a person from Cheyenne is stronger, than the one of somebody from LA..
In history it was very common, that voters were divided into curias, according to their social position. Each curia voted seperatedely, so a vote of a peasent or a shopkeeper could be much weaker than the vote of an aristocrat.
It makes sense in English if the person saying the sentence is an electoral candidate.
Read the sentence above so: ”My vote is too weak to be able to change anything”. Has it sense?