I have no side in this debate because I don't support any of the potential candidates, but since US politicians are not effectively disciplined by their base but rather by their donors, it's quite reasonable for the base to seek evidence of past commitment to issues they prioritize. It's a very poor heuristic, but it's all they've got. As you said, the politicians are doing a job, but they don't take their orders from the voters. The system is utterly ruined.