On August 23, 1864, Abraham Lincoln met with his cabinet. He circulated amongst his ministers a folded piece of paper, and asked them to sign it without looking at its contents. They did (as the LOC website is down until tomorrow, the image will appear here then).
Inside, one would have found the following words:
Washington, Aug. 23, 1864.
This morning, as for some days past, it seems exceedingly probable that this Administration will not be re-elected. Then it will be my duty to so co-operate with the President elect, as to save the Union between the election and the inauguration; as he will have secured his election on such ground that he can not possibly save it afterwards.
Coming just days after Lincoln had set aside suggestions that he abandon emancipation in the Confederacy as a war aim, this memorandum suggests that the president did not think his chances for reelection were very good.
Allen Guelzo offers his take here: