[4] Historians such as Wood Gray, Jennifer Weber and Kenneth M. Stampp[citation needed] have argued that it represented a traditionalistic element alarmed at the rapid modernization of society sponsored by the Republican Party and that it looked back to Jacksonian democracy for inspiration.

Weber argues that the Copperheads damaged the Union war effort by opposing conscription, encouraging desertion, and forming conspiracies.

[5][6][page needed] Historians such as Gray and Weber argue that the Copperheads were inflexibly rooted in the past and were naive about the refusal of the Confederates to return to the Union.

[7] In turn, the Copperheads became a significant target of the National Union Party in the 1864 presidential election, when they were used to discredit the leading Democratic candidates.

A possible origin of the name came from a New York Times newspaper account in April 1861 that stated that when postal officers in Washington, D.C., opened a mail bag from a state now in the Confederacy: A day or two since, when one of the mail-bags coming from the South by way of Alexandria, was emptied in the court-yard of the Post-office, a box fell out and was broken open, – from which two copperheads, one four and a half and the other three feet long, crawled out.

[13] The New York Journal of Commerce, originally abolitionist, was sold to owners who became Copperheads, giving them an important voice in the largest city.

In the spring and summer of 1863, the paper urged its Irish working-class readers to pursue armed resistance to the draft passed by Congress earlier in the year.

Wisconsin newspaper editor Marcus M. Pomeroy of the La Crosse Democrat referred to Lincoln as "Fungus from the corrupt womb of bigotry and fanaticism" and a "worse tyrant and more inhuman butcher than has existed since the days of Nero ...

The man who votes for Lincoln now is a traitor and murderer ... And if he is elected to misgovern for another four years, we trust some bold hand will pierce his heart with dagger point for the public good".

As war opponents, Copperheads were suspected of disloyalty, and their leaders were sometimes arrested and held for months in military prisons without trial.

Indiana Republicans then used the sensational revelation of an antiwar Copperhead conspiracy by elements of the Sons of Liberty to discredit Democrats in the 1864 House elections.

The military trial of Lambdin P. Milligan and other Sons of Liberty revealed plans to set free the Confederate prisoners held in the state.

This convention adopted a largely Copperhead platform and selected Ohio Representative George Pendleton, a Peace Democrat, as the vice-presidential candidate.

[19][20] They were most numerous in border areas, including southern parts of Ohio, Illinois, and Indiana (in Missouri, comparable groups were avowed Confederates).

[22] The Copperhead coalition included many Irish American Catholics in eastern cities, mill towns and mining camps (especially in the Pennsylvania coal fields).

On the stump his hot temper, passionate partisanship, and stirring eloquence made an irresistible appeal to the western Democracy [i.e. the Democratic Party].

His bitter cries against protective tariffs and national banks, his intense race prejudice, his suspicion of the eastern Yankee, his devotion to personal liberty, his defense of the Constitution and State's rights faithfully reflected the views of his constituents.

[24]Two central questions have run through the historiography of the Copperheads: "How serious a threat did they pose to the Union war effort and hence to the nation's survival?"

Klement argued in the 1950s that the Copperheads' activities, especially their supposed participation in treasonous anti-Union secret societies, were mostly false inventions by Republican propaganda machines designed to discredit the Democrats at election time.

[25][30][page needed] Jennifer Weber's Copperheads: The Rise and Fall of Lincoln's Opponents in the North (2006) agrees more with Gray and Milton than with Klement.

Third, Weber concluded that the peace movement deliberately weakened the Union military effort by undermining both enlistment and the operation of the draft.

The soldiers' rejection of Copperheadism and overwhelming support for Lincoln's reelection in 1864 was decisive in securing the Northern victory and the preservation of the Union.