the committee admission is to find out what happened before during and after the attack on the u.s. consulate in libya when mrs. clinton was secretary of state and longest running select committee investigation in u.s. history and been accused of targeting clinton to hurt her presidential campaign. mrs. clinton spent the week preparing instead of campaigning and knows she ll face tough questions but she s battle tested. tom foreman takes a look. reporter: since the killing of four americans in benghazi in 2012, in all the congressional grilling, hillary clinton let her frustration show in a big way only once. was it because of a protest or four guys out on a walk to decide to kill americans. what difference at this point does it make? aside from that her testimony is marked by steady nerves even amid withering attacks. you let the consulate become a death trap. and that s national security malpracti malpractice. reporter: that s what led her