The party divided during the 1864 presidential campaign, with different elements supportive of the candidacies of Abraham Lincoln, George B. McClellan, and Salmon Chase, respectively.
In the 1859 Kansas gubernatorial election, the Republican Charles L. Robinson defeated the Democratic outgoing territorial governor Samuel Medary with 59 percent of the vote.
On September 29, a meeting of War Democrats and anti-Lane Republicans calling themselves the Union State Convention gathered at Lawrence, Kansas and nominated a statewide ticket, with Marcus J. Parrott for Congress and William R. Wagstaff for governor.
They accused the Lane faction of fostering partisanship and dividing the public in a time of war and of using "open pecuniary bribery" to cement their grip on political power.
[7] Parrott's nomination proved a liability for the Union Party when the candidate mocked the threat from Confederate guerrillas in an appearance with Lane at Leavenworth, Kansas.
"[9] Overwhelmed by attacks from their opponents and the press, weighted down by Robinson's unpopular administration, Wagstaff carried just two counties and 35% of the vote in the gubernatorial race, while Parrott was handily defeated by A. Carter Wilder in the concurrent congressional election.
[12] Meanwhile, the national Lincoln administration, with which Lane was politically aligned, faced growing internal opposition in the form of Salmon P. Chase's presidential candidacy.
Radical Republicans in the Union Party hoped Chase's election would give them access to federal patronage denied by Lincoln and yield a more aggressing prosecution of the sagging war effort.
At the Topeka convention, the Kansas War Democrats and anti-Lane Republicans met separately to nominate electors for the presidential election before convening in joint session to select candidates for state offices.
Following Lincoln's assassination in April 1865, Johnson, his successor, laid claim to the National Union Party and attempted to remake it as a vehicle for his own political ambitions.