"Political scientists have been studying the question of campaign…

"Political scientists have been studying the question of campaign promises for almost 50 years, and the results are remarkably consistent. Most of the literature suggests that presidents make at least a “good faith” effort to keep an average of about two-thirds of their campaign promises; the exact numbers differ from study to study, depending on how the authors define what counts as a campaign promise and what it means to keep it."

https://fivethirtyeight.com/features/trust-us-politicians-keep-most-of-their-promises/