President Obama and Mitt Romney, the Republican who wants his job, face off in three 90-minute debates this month – starting Wednesday at a University of Denver sports arena. This week's event focuses on the economy for half the time and then on other domestic issues such as health care and the role of government.

Each candidate is practicing at mock debates with advisers. At Obama's drills, the role of Romney is filled by John Kerry, a Democratic senator from Massachusetts who has home-state familiarity with the former Republican governor. At Romney's rehearsals, Ohio Sen. Rob Portman stands in for the president. "Debates can be a defining moment for a presidential candidate," says CNN correspondent Jack Cafferty, "and Oct. 3 will be huge." At the University of Akron in Ohio, political scientist David Cohen says it this way: "I am definitely going to get my popcorn out for these debates."

Each will be televised by major networks from 9-10:30 p.m. Eastern time. Jim Lehrer of PBS moderates this Wednesday's leadoff, followed by a vice-presidential candidates' debate between Joe Biden, the Democrat now in office, and Congressman Paul Ryan on Oct. 11 at Centre College in Kentucky. The second presidential showdown is at Hofstra University in New York, where Candy Crowley of CNN moderates a town hall-style debate with citizens asking questions about foreign and domestic issues. In the Oct. 22 finale ar Lynn University in South Florida, Bob Schieffer of CBS will preside over a foreign policy debate.

Debate organizer says: "[The] intention is to have the candidates come prepared for a more in-depth conversation." – Janet Brown, Commission on Presidential Debates executive director, explaining the first-time announcement of topics in advance

Journalist says: "Civics teachers won’t want to hear this, but the easiest way to judge 'victory' in many debates is to watch with the sound turned off so you can assess the candidates’ ease, tenseness, humor and other traits signaled by their body language." – James Fallows, national correspondent for The Atlantic magazine

Civic group leader says: "Debates are still an invaluable opportunity for voters to get first-hand information from the candidates." -- Elisabeth MacNamara, League of Women Voters national president