Answer:
declared their opposition to slavery.
Step-by-step explanation:
In 1856, two years after the formation of the Republican Party in 1854 Wisconsin. The Republican party presented John C. Fremont as the party's presidential candidate.
Even though the party lost to the Democratic Party who presented James Buchanan. Republicans centered their campaign on anti-slavery, by declaring their "opposition to slavery."
This made them win a majority of the Northern votes at the time.