The nominee is being questioned by a number of people concurrently. Group dynamics are a key factor, with various individuals bringing their own interests and agendas to the table. You've got everything from those who are like-minded (lobbing consistently easy questions) and those who are more interested in hearing themselves talk than the nominee, to those who are skeptical or even downright antagonistic.
There are multiple distractions. Photographers (sometimes lots of photographers) are sitting on the floor in direct view, snapping away. Then there are the television cameras. Aides walk in and out of the proceedings.
Depending on the nominee and the circumstances (tax troubles, anyone?), it can be a pressure cooker. Especially when the nominee runs into trouble, every word is scrutinized. Questioners are looking for holes in statements, or inconsistencies - mistakes they can pounce on.
Talk about a hot seat.
While you're not going to be grilled by the Senate and show up on the news, in many ways these confirmation hearings parallel panel interviews you might face. Group interviews can be quite challenging, intimidating, and stressful. In fact, this is generally their purpose. They're designed to see how well you deal with a high-pressure situation while facing multiple questioners.
Add to that the inevitable agendas of at least some of the interviewers, and you've got waters that could be difficult to navigate. You'll prepare for this interview just as you would for a conversation with a single person; however, when answering, you need to stay focused on the entire group. Respond initially to the person who asked the question, but be sure to acknowledge the other panelists by briefly making eye contact while you're talking. Return your focus to the questioner as you're completing your answer.
Because a number of people are in the room, there are bound to be distractions. Rustling paper, movement of people, coughing, someone pouring ice water into a glass...whatever might be going on, don't allow your surroundings to divert your attention.
It's not uncommon in these settings for subordinates to attempt to "stump" you or make you uncomfortable. (Typically this is done by asking irrelevant, extraneous questions.) The motive? Often it's to highlight their self-perceived superiority. It's viewed as a golden opportunity to publicly "one up" both the candidate and their peers - and so much the better if executive management is in the room.
If you understand how to deal with challenging interviewers, though, then you'll know how to maintain your composure and manage a less-than-desirable situation.
Whether it's a panel setting or one-on-one, your goal is the same. You've got to showcase your skills and highlight why you're the best person for the job...and you have to demonstrate that you can perform under pressure.