In this letter, Lincoln is discussing charges that the editors of the Daily Chicago Times made regarding his actions in the U.S. House of Representatives related to a bill providing for supplies for U.S. military personnel serving in the Mexican War. The editors claimed that Lincoln, whom the Republican Party had recently nominated as their candidate for the U.S. Senate, voted against the bill in an effort to deny food, clothing, medicine, and medical care to U.S. soldiers and officers serving at the front. This was not true. Although Lincoln opposed the Mexican War and questioned its constitutionality during his time in the U.S. House, he nevertheless voted in favor of supplies for U.S. troops on at least two occasions: February 17, 1848 and March 8, 1848. In both instances, the bills Lincoln voted for passed the U.S. Senate and became law, funneling aid in the form of money, food, clothing, medical supplies, and the like to U.S. military personnel serving in Mexico.

Joseph Medill and John L. Scripps also wrote to Lincoln to inform him of the Daily Chicago Times' attacks on his congressional record related to the Mexican War and asked Lincoln for a response. Lincoln replied to Medill on June 25, asserting that he never "gave any vote for withholding any supplies whatever, from officers or soldiers of the Mexican war." Despite publication of the facts surrounding Lincoln's voting record in the U.S. House in the Illinois press as early as June 25, 1858—including by Democratic newspapers, Stephen A. Douglas, Lincoln's opponent for the U.S. Senate, repeated the Daily Chicago Times' claims during the election campaign of 1858. In speeches he delivered during the campaign, including during the Lincoln-Douglas debates, Lincoln repeatedly refuted the charges and cited congressional records to back up his voting record in the U.S. House.

In the end, Douglas won reelection to the U.S. Senate. Through the campaign, however, and in particular through his participation in the Lincoln-Douglas debates, Lincoln gained recognition as well as standing within the national Republican Party.