In the US if you give a politician money in exchange for voting against a bill, it's illegal (it's called "quid-pro-quo" in lawyer terms)
But if you just donate money to the politician, his family, or his campaign, without requesting anything - and then he "coincidentally" happens to vote against the bill which you didn't want, it is perfectly legal.
Basically, many politicians are regularly doing something clearly unethical and corrupt in a technically "legal" way.
Yeah but you literally can't prove most of these are bribery. The whole point of donating to a campaign is to support someone you agree with. That politician may vote the same way, whether you support them or not. The "support" is meant to get them into office to do things you want.
The real problem is illegal cooperation between candidates and their superpacs and no meaningful limits on donations to superpacs. Citizens United allowed unlimited donations. Without this, bribery would be very hard. You would have to literally give them money or houses (like Clarence Thomas), or jobs to their family (also Clarence Thomas).
With real campaign finance limits you could directly tell a politician "I want to bribe you" and they would ignore it. Most police officers don't take bribes because the risk of losing their nice jobs is too great.
That's the point, the letter of the law means you have to meet a set criteria to prove it. The spirit of the law can look at it and go 'hey you got this donation, and proceed to act in this corporate interest' and see the pattern of abuse is acting against the conceptual idea of not being able to be bribed.
Without this, bribery would be very hard. You would have to literally give them money or houses (like Clarence Thomas), or jobs to their family (also Clarence Thomas).
Those are actually very hard to get away with. There's just no direct oversight of the Supreme Court.
And it's not illegal to help constituents. That's literally the purpose of Senators and Representatives in Congress. Your solution would mean that if you donated to AOC and told her "I like your point of view, vote based on that" she would be required to change her vote to the opposite of what you want.