After the midterm trouncing, President Obama is probably looking forward to flying to Seoul to attend the G-20 economic summit this week. But it's starting to look like a really big headache, mostly because of cars. Before attending, Obama had hoped to get Congress's approval of a new free-trade pact with South Korea. But that nation's refusal to budge on allowing more U.S. auto sales has stalled action. Now he faces an embarrassing episode at the summit. Hyundai-Kia is providing bulletproof Equus limos for visiting leaders, and Obama is expected to ride in one. Does he irk his host and snub the car? Or does he risk the wrath of Detroit's carmakers and autoworkers who have been pressuring the president to stick to his Cadillac limo? One auto exec offers a solution: a brief sit in an Equus, then back into the Caddy.