One of the reasons Heinlein is quoted so much  is because he's always right about people. (For "reform" politician, read "progressive")

All it takes to get [a reform politician] to break his word is for someone to get his ear and convince him that it is necessary for the greater good of all the peepul

After talking about honest politicians staying bought

But a reform politician has no such lodestone. His devotion is to the welfare of all the people–an abstraction of very high order and therefore capable of endless definitions. If indeed it can be defined in meaningful terms. In consequence your utterly sincere and incorruptible reform politician is capable of breaking his word three times before breakfast–not from personal dishonesty, as he sincerely regrets the necessity and will tell you so–but from unswerving devotion to his ideal.

And the most scary, considering my contention that we're in the Funniest End of Civilization Ever

After he gets hardened to this, he’s capable of cheating at solitaire. Fortunately he rarely stays in office long–except during the decay and fall of a culture.”

And that's an honest progressive politician, a vanishingly small breed.