Complex sentence: As a candidate in 2007, Tsongas promised withdrawing troops and ending the Iraq War: which her first bill introduced aimed to do by implementing a timetable for withdrawal from Iraq, however it died in committee.
Split into simpler sentences: As a candidate in 2007, Tsongas promised to withdraw troops and end the Iraq War. The first bill she introduced aimed to do this by implementing a timetable for withdrawal from Iraq; however, the bill died in committee.