Though campaign donations for advertising? Or bribery?
Both, and more. The US State is designed against change, and the only parties of any federal relevance are the DNC and GOP, who are aligned in service to their donors, and maintain close business ties to the defense industry and banks.
Why do you think voting in national elections doesn’t matter?
Because the US is designed in a manner where you choose which of two far-right parties to support. The DNC always positions themselves as not quite as right wing as the GOP, so no matter how far right the GOP swerves, the DNC trails just behind.
Combined with major issues such as the electoral college, most votes don’t even have an influence on which of the two far-right parties wins, only those in swing states. The only election that matters for the vast majority are local elections.
Electoralism has been a dead strategy for Leftists for centuries, it’s an answered question and the answer is no, Revolution is necessary to enact change.