Complex sentence: He became a Democrat after the Whig party had ceased to exist, he was debarred from a political career in his own state, where his party was in the minority, but he served in the state constitutional convention in 1870.
Split into simpler sentences: He became a Democrat after the Whig party had ceased to exist. He was debarred from a political career in his own state, where his party was in the minority, but he served in the state constitutional convention in 1870.