Complex sentence: Senator Trent Lott (R-Miss.) first called the option "nuclear" in March 2003; the metaphor of a nuclear strike refers to the majority party unilaterally imposing a change to the filibuster rule, which might provoke retaliation by the minority party.
Split into simpler sentences: Senator Trent Lott (R-Miss.) first used the term "nuclear option" for this maneuver in March 2003. The metaphor of a nuclear strike refers to the majority party unilaterally imposing a change to the filibuster rule, which might provoke retaliation by the minority party.