Who said all our great presidents were leaders of thought at times when certain historic ideas in the life of the nation had to be clarified?

Explanation:

The Presidency is not merely an administrative office. That’s the least of it. It is more than an engineering job, efficient or inefficient. It is pre-eminently a place of moral leadership. All our great Presidents were leaders of thought at times when certain historic ideas in the life of the nation had to be clarified.

this is a false claim the emancipation proclamtion freed all slaves in the rebillion states