This approach to rhetoric could be aptly labelled as [honesty][1]honesty:
The quality of being honest
It is a rare thing to find in political oratory, but is a stratagem by which the speaker incurs the cost by being truthful in one matter, increasing the trust of his audience, so that they are more apt to believe in what he says next. [1]: http://www.oxforddictionaries.com/definition/english/honesty