bolt

The Japan Times Online, March 2 の記事です。
Masuzoe issues reform ultimatum to ailing LDP Veteran lawmaker Yoichi Masuzoe issues what could be taken as an ultimatum to his ailing Liberal Democratic Party, saying a failure to restructure will not only push the public to abandon it but may force its ranks to bolt as well.
この "bolt" ですが、 "nut and bolt" とか　"bolt from the blue" しか思い浮かばないので意味が分かりませんが、新聞記事なので先を読みます。 　
The trend could spark some members to force Tanigaki out of his seat, he warned, while also touching on the possibility of creating a new party himself.
"its ranks" はLDP Memberを指しているので "bolt" はここでは余り良くない意味になることが想像できます。　ここで辞書を引きます。
・OneLook Quick Definitions: run away; usually includes taking something or somebody along
・Dictionary.com: 1.(used with object) to discontinue support of or participation in; break with: to bolt a political party. 2. (used without object) to break away, as from one's political party.
なるほど "bolt" が出てくる訳が分かりました。