Give the maximum to 18 candidates, but not 19?

Federal law limits citizens to contributing no more than $2,600 to any one candidate’s campaign. With the aggregate $48,600 limit on candidate contributions, that means individual contributors would only be able to support 18 candidates to the legal maximum. Once contributors reach the limit on candidate contributions, the law bans them from giving a penny more, with violations garnering up to a five-year prison sentence. If the first 18 candidates aren’t corrupted by accepting the maximum contributions, what is so different about candidate number 19?