It's usually difficult to prove beyond a reasonable doubt that a campaign contribution influenced a public official to take an official action. That's why other ways to limit the influence of money in politics, such as disclosure rules and limits on contributions, are so important.
But sometimes the link between cause and effect is so clear that a politician can be convicted of criminal bribery. The Supreme Court last week wisely refused to make such convictions harder to achieve.
Read the rest of the story at the Los Angeles Times.