Complex sentence: Elections to the United States Senate were held on November 6,2012, with 33 of the 100 seats in the Senate being contested in regular elections whose winners will serve six-year terms from January 3,2013 until January 3,2019.
Split into simpler sentences: Elections to the United States Senate will be held on November 6,2012, with 33 of the 100 seats in the Senate being contested. Since Senators are elected for six-year terms, those elected will serve from January 3,2013 until January 3,2019.