Complex sentence: Davis' weak stance on slavery began to cause a decrease in his popularity as abolitionist sentiment in the state gained ground during the 1840s, and he refused to support Webster in his 1852 presidential bid, campaigning on behalf of Winfield Scott.
Split into simpler sentences: Davis' weak stance on slavery began to cause a decrease in his popularity as abolitionist sentiment in the state gained ground during the 1840s. He also refused to support Webster in his 1852 presidential bid, campaigning on behalf of Winfield Scott.