Abraham Lincoln was the Republican candidate from Illinois for the U.S. Senate in 1858, running against Democrat Stephen A. Douglas, the incumbent. At this time the Illinois General Assembly elected the state’s representatives in the U.S. Senate, thus the outcome of races for the Illinois House of Representatives and Illinois Senate in the election of 1858 were of importance in the campaign. Lincoln and Douglas both focused their campaign efforts on the former Whig stronghold of central Illinois, where the state legislative races were the closest. See the 1858 Illinois Republican Convention; 1858 Federal Election. On July 7, Lincoln wrote to his former congressional colleague John J. Crittenden of Kentucky to ask whether rumors of Crittenden’s support for Douglas were true. An eminent former Whig, Crittenden was widely regarded as the natural successor to Henry Clay, and Lincoln worried that a Crittenden endorsement for Douglas would hurt his chances with his former Whig brethren in Illinois. Crittenden welcomed Lincoln's rise to political prominence, but had little sympathy with the Republican Party. Crittenden responded on July 29, assuring Lincoln that he was remembered favorably. Crittenden explained, however, that he and Douglas, though always belonging to different political parties and "opposed, in politics, to each other," shared a strong aversion to the Lecompton Constitution. The Buchanan administration's harsh response to Douglas and use of its power to prevent his reelection brought sympathy from Crittenden. He wrote of Douglas, "I could not but wish for his success— and his triumph over such a persecution– I thought that his reelection was necessary as a rebuke to the Administration, and a vindication of the great cause of popular rights & public justice." Crittenden admitted that he had shared his support of Douglas in various conversations but that he had only sent a handful of letters in which "Mr Douglas was alluded to and recommended." Going forward, he wrote, he could not promise anything, only that, "Whatever my future course may be, I trust that I shall so act as to give no just cause of offence to any candid & liberal friend, even tho' he may differ with me in opinion."

Though expressing "no disposition for officious intermeddling" in his letter to Lincoln, Crittenden nonetheless became embroiled in the campaign for the U.S. Senate. On July 19, T. Lyle Dickey, a former Whig and Lincoln supporter who had defected to the Democrats and Douglas, wrote Crittenden requesting that he confirm a conversation with Dickey in April 1858 where Crittenden praised Douglas. On August 1, Crittenden wrote Dickey confirming the conversation and his praise for Douglas's service to Illinois and his principled position on the Lecompton Constitution. Not wishing to be appear "to be an officious intermeddler" in the election, Crittenden requested that Dickey, should he speak of the conversation or letter, "acquit me of any intermeddling, or of the presumption of seeking to obtrude myself or my sentiments upon the attention of the people of Illinois." Dickey kept the letter private until October 19, when he read it aloud in a speech denouncing Lincoln for abandoning Clay and Whiggery. The Daily Illinois State Journal sought to mitigate the damage by claiming that Crittenden's letter to Dickey was a forgery and by suggesting that Crittenden had written Lincoln--presumably Crittenden's letter of July 29--supporting opposition against Douglas. The Daily Missouri Republican demanded that Lincoln publish this letter. The Illinois State Journal continued to misrepresent Crittenden's correspondence to Lincoln, prompting Owen G. Cates of Saint Louis to write Crittenden asking if he wrote such a letter. On October 28, Crittenden responded in a telegram: "I have written no such letter." Crittenden's letter to Dickey, Dickey's speech, and Crittenden's subsequent telegram hurt Lincoln in the old Whig stronghold of Central Illinois, contributing to Democrats retaining control of the General Assembly, allowing Douglas to win reelection.