When President Franklin D. Roosevelt made plans to run for a third term in 1940 he decided to drop conservative Vice President John Nance Garner from the ticket...Instead Roosevelt chose Secretary of Agriculture Henry Wallace. However, many of Garner's fellow conservative Democrats...despised Wallace for his liberalism and attempted to block his nomination at the convention...
Below is the letter which Roosevelt drafted, in which he vowed not to run if his fellow Democrats blocked his choice of Wallace. (In the end the letter was never sent, as a speech by Eleanor Roosevelt turned the tide for Wallace at the convention.) Roosevelt's letter, with its powerful critique of the Democratic Party, was published almost nowhere and was essentially unknown before it appeared in Oliver Stone's Showtime documentary series Untold History of the United States...
http://www.michaelmoore.com/words/m...er-declining-1940-democratic-party-nomination
Franklin D. Roosevelt Letter to the Democratic Convention
July 18, 1940
Members of the Convention:
In the century in which we live, the Democratic Party has received the support of the electorate only when the party, with absolute clarity, has been the champion of progressive and liberal policies and principles of government.
The party has failed consistently when through political trading and chicanery it has fallen into the control of those interests, personal and financial, which think in terms of dollars instead of in terms of human values.
The Republican Party has made its nominations this year at the dictation of those who, we all know, always place money ahead of human progress.
The Democratic Convention, as appears clear from the events of today, is divided on this fundamental issue. Until the Democratic Party through this convention makes overwhelmingly clear its stand in favor of social progress and liberalism, and shakes off all the shackles of control fastened upon it by the forces of conservatism, reaction, and appeasement, it will not continue its march of victory.
It is without question that certain political influences pledged to reaction in domestic affairs and to appeasement in foreign affairs have been busily engaged behind the scenes in the promotion of discord since this Convention convened.
Under these circumstances, I cannot, in all honor, and will not, merely for political expediency, go along with the cheap bargaining and political maneuvering which have brought about party dissension in this convention.
It is best not to straddle ideals.
In these days of danger when democracy must be more than vigilant, there can be no connivance with the kind of politics which has internally weakened nations abroad before the enemy has struck from without.
It is best for America to have the fight out here and now.
I wish to give the Democratic Party the opportunity to make its historic decision clearly and without equivocation. The party must go wholly one way or wholly the other. It cannot face in both directions at the same time.
By declining the honor of the nomination for the presidency, I can restore that opportunity to the convention. I so do.
*cough* 
even from more "Center-left" types. 
