Complex sentence: Chase, a former Democrat, had alienated many of the former Whigs by his coalition with the Democrats in the late 1840s, had opposed tariffs demanded by Pennsylvania, and critically, had opposition from his own delegation from Ohio.
Split into simpler sentences: Chase, a former Democrat, had alienated many of the former Whigs by his coalition with the Democrats in the late 1840s. He had also opposed tariffs demanded by Pennsylvania, and critically, had opposition from his own delegation from Ohio.