To advance from a congressman to a senator requires not only ability but also publicity to gain voter recognition.
Publicity requires substantial funds.
Election funding, Campaigns, Promotional activities,
Hardly anyone could afford these alone.
Funds mostly come from 'political donations.'
Political donations are legal.
A fund is set up for public donations, used for campaign purposes, but public donations are minimal compared to the vast sums needed, often surpassed by contributions from major benefactors.
Every politician has one or more major benefactors, the higher the level, the more benefactors.
But taking such funds comes with obligations. Benefactors expect returns on their investments.
If you don't deliver, they might stop funding you.
