At a very selective and affluent university, my understanding is that you need to give LOTS of money before it changes an admissions decision. In some cases, modest donations or alumni parents may just earn you a wait list spot instead of the denial you would have otherwise received. That is why some universities have HUGE wait lists.
One admissions officer said “The more famous or powerful a person is who recommends an applicant, the less they really know about the applicant.” That admissions officer said they would much rather receive a recommendation from a teacher who knows the student very well than from a powerful politician who knows very little about the student.
Remember what happened when Mrs. Soprano tried to get a recommendation for Georgetown for her daughter?