Complex sentence: Thorndyke plans to use her newspaper chain's influence to deadlock the 1948 Republican National Convention, so it will choose Matthews as a compromise dark horse candidate instead of Dewey, Taft, or another.
Split into simpler sentences: Thorndyke plans to use her newspaper chain's influence to deadlock the 1948 Republican National Convention. The Party is to choose Matthews as a compromise dark horse candidate instead of Dewey, Taft, or another.