Complex sentence: He was initially a huge underdog, but a Green candidate siphoned off enough votes from the Democratic candidate, state Insurance Commissioner Eric Serna, who was also deeply unpopular with voters in the district, to allow Redmond to win by only 3,000 votes.
Split into simpler sentences: He was initially a huge underdog even though the Democratic candidate, state Insurance Commissioner Eric Serna, was deeply unpopular with voters in the district. However, a Green candidate siphoned off enough votes from Serna to allow Redmond to win by only 3,000 votes.