Complex sentence: In 2014, he was the Democratic candidate for the U.S. Senate seat to be vacated by Mike Johanns; he lost the election to Republican Ben Sasse, taking 31% of the vote to Sasse's 65%.
Split into simpler sentences: In 2014, he was the Democratic candidate for the U.S. Senate seat to be vacated by Mike Johanns. He lost the election to Republican Ben Sasse, taking 31% of the vote to Sasse's 65%.