[求助]LSAT-4-1-21 这段看不懂--丑闻的power

看不懂incumbents 为什么要reelction? return to office 什么意思？彻底晕了。。。这段讲的是什么？

21. Whenever a major political scandal erupts before an election and voters blame the scandal on all parties about equally, virtually all incumbents, from whatever party, seeking reelection are returned to office. However, when voters blame such a scandal on only one party, incumbents from that party are likely to be defeated by challengers from other parties. The proportion of incumbents who seek reelection is high and remarkably constant from election to election.

If the voters' reactions are guided by a principle, which one of the following principles would best account for the contrast in reactions described above?

不愧为lawyer No.1, Lsat 专家，多谢！