President Barack Obama is on his way to Copenhagen on Air Force One — where he will meet the First Lady, and they will make their case for Chicago to host the 2016 Summer Olympics. It is the first time an American president has taken such a step. Chicago faces stiff competition from Tokyo, Rio de Janeiro and Madrid. Bookkeepers are currently giving Chicago the edge over Rio. The International Olympic Committee will announce the host city tomorrow at 12:30 p.m. eastern. So tonight, we ask: Which city is going to win? Tell us what you think. You can follow "Nightline" anytime on Twitter: http://twitter.com/Nightline.