Complex sentence: Nothing but Cicero's wish to do a favour to Pompey could have induced him to take on the task; it is hinted that the half-heartedness of the defence contributed to Gabinius's condemnation.
Split into simpler sentences: Nothing but Cicero's wish to do a favour to Pompey could have induced him to take on the task. Commentators hint that the half-heartedness of Cicero's defence contributed to Gabinius's condemnation.