What political party pioneered the use of slogans in political campaigns?

Answer 1

It's not clear that any one party became known for this, since the practice evolved over time. But one of the earliest (and most successful) campaign slogans that we know about goes back to 1840, and the Whig party. The Whigs used the slogan "Tippecanoe and Tyler Too" to promote William Henry Harrison, whose nickname came about when he was a military officer who won a great victory at the Tippecanoe River in the Indiana Territory. His running mate was John Tyler, and thus the slogan.

Answer 2

Whig