WASHINGTON » Think of today’s presidential debate as a championship fight rematch.

Republican challenger Mitt Romney won the first bout, as President Barack Obama failed to counterpunch.

Then came what’s known in boxing as the undercard, the vice presidential debate. Incumbent Joe Biden came out swinging at the opening bell, although GOP challenger Paul Ryan counterpunched just as hard. Obama-Biden supporters were relieved.

The Obama campaign promises the president will be more aggressive today. But this time the candidates and the moderator won’t be the only people in the ring when the 90-minute debate begins at 3 p.m. Hawaii time.

Q. Why is that?

A. Continuing a format that began 20 years ago, this is the "town hall" debate where people representing a cross-section of America get to ask the questions.

Q. Can people in the audience simply raise their hands and be called upon at random?

A. No. That’s one thing that changed since the first presidential town hall debate in 1992, when questions and questioners weren’t screened beforehand.

Q. So how does the screening work?

A. The Gallup polling organization picks about 80 uncommitted voters. Those voters will work with moderator Candy Crowley of CNN, and she decides who in the group will get to ask a question. Crowley said she and a small team of helpers will try to get as broad a range of questions as possible and nobody else will know the questions in advance.

Q. How did Gallup choose the participants?

A. They were recruited as part of a random sample of all residents living in Nassau County, N.Y. Each resident contacted was asked a series of questions. Those who met the criteria as uncommitted voters were invited to participate.

Q. Will the candidates be seated?

A. They’ll have chairs, but will spend most of their time as close as possible to the audience, walking around and looking directly at the questioner. Think of it as trying to connect with citizens who are there to represent millions of Americans watching on television.

Q. How will the audience be seated?

A. The group of 80 will be in three rows of circular risers facing the candidates, with an open space in the middle. Off camera, there will be a larger audience in the arena at Hofstra University in Hempstead on New York’s Long Island.

Q. In the presidential and vice presidential debates so far, one candidate got the first question and the other candidate had the last word. Will that change tonight?

A. Yes. There are no opening and closing statements. Romney gets the first question. Each candidate is supposed to have two minutes to respond, after which Crowley will facilitate a two-minute discussion. If the earlier debates are an indication, don’t expect the candidates to stick to those strict time limits.

Q. Wasn’t there an attempt to limit the moderator’s role in this debate?

A. Yes. The two campaigns came to an understanding that Crowley’s role should be limited, so that she wouldn’t use the discussion period to introduce a new topic or rephrase a question.

Q. Will that affect the debate?

A. No. The campaigns left two crucial entities out of the agreement: Crowley and the Commission on Presidential Debates, which runs the debate program. Frank J. Fahrenkopf, Jr., co-chairman of the commission, said: "I don’t care what it says since we’re not party to it."