Paul Ryan prepares to take on skilled debater Joe Biden Thursday

Ryan aides note that more people watched Biden's 2008 debate against then-Gov. Sarah Palin, the GOP vice presidential nominee, than any of Obama's debates against Republican John McCain. But that was as much about Palin's celebrity and curiosity about her and not the weight of the vice presidents' roles.

This time, Republicans have nominated a wonk who is a walking collection of think tank studies — not a first-term governor from Alaska like Palin.

Ryan and Olson practiced three times before heading into more intense sessions in the Virginia mountains. They wore suits and ties and dined on room service in Washington hotels for two sessions, then donned plaid shirts and ate Jimmy Johns sandwiches at the other session in Ryan's hometown of Janesville, Wis.

In Virginia, they simulated the debate setting.

Kerry Healey, who was Romney's lieutenant when he was governor of Massachusetts and now advises him on foreign policy, stood in for debate moderator Martha Raddatz of ABC News and even channeled the newswoman's speaking style.

Ryan has tried to keep the number of advisers in the room with him to fewer than 10. From time to time, Romney aides from the Boston campaign headquarters joined the preparations, including strategist Russ Schriefer, longtime loyalist Beth Myers and conservative liaison Peter Flaherty. Foreign policy hand Dan Senor also has been helping Ryan.

Ryan hasn't debated since his first run for Congress — in 1998 at age 28.