Could George B. McClellan have become the seventeenth President of the United States? It certainly appeared to be a possibility as Abraham Lincoln assessed the military and political landscape in summer 1864.

President Lincoln understood that his chances of reelection in November hinged on military success in a war now in its fourth year. By summer 1864, Gen. Ulysses S. Grant had settled in for a prolonged siege against the Confederates near Petersburg, Va., and Gen. William T. Sherman made slow progress toward Atlanta. Confederate general Jubal A. Early, meanwhile, had led his troops to the outskirts of Washington, D.C., in July. The war effort seemed to have stalled for the Union, and the public blamed President Lincoln.

The political news for Lincoln was no brighter. The Republican Party was divided, especially about emancipation. Some Republicans thought Lincoln had gone too far; others not far enough. And the Democrats had not yet held their nominating convention, so the Republicans did not know for sure who their opponents would be or the platform they would run on.

It was in this context that Abraham Lincoln wrote the following memorandum on 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. — A. Lincoln

Lincoln folded the memorandum and pasted it closed, so that the text inside could not be read. He took it to a cabinet meeting and instructed his cabinet members to sign the outside of the memo, sight unseen, which they did. Historians now refer to this document variously as the “Blind Memo” or “Blind Memorandum” because the cabinet signed it “blind.” In so doing the Lincoln administration pledged to accept the verdict of the people in November and to help save the Union should Lincoln not be reelected.

As if on cue, Lincoln’s fortunes began to change. The Democrats nominated McClellan for president on August 30 but saddled him with a “Copperhead” peace Democrat, Rep. George H. Pendleton of Ohio, as a running mate. The Democratic platform declared the war a failure and urged that “immediate efforts be made for a cessation of hostilities,” which even McClellan could not fully support. Then Gen. Sherman scored a tremendous victory when Atlanta fell to the Union on Sept. 2.

The brighter military outlook, expert political maneuvering by Lincoln and his reinvigorated party, and the negatives associated with McClellan and the Democrats spelled victory at the polls for the Republicans. Safely re-elected, Lincoln brought the memorandum with him to the next cabinet meeting on November 11. He finally read its contents to the cabinet, reminding them it was written “when as yet we had no adversary, and seemed to have no friends.”

The Blind Memorandum reminds us not to read history backwards, with knowledge of how things turned out. People only know what they know at the time. The primary sources they leave behind help us understand what they knew, thought, and felt at the time, and how they interpreted their own world. What would you predict in the future based on what you know today?