DENVER – Mitt Romney spent much of Tuesday near his hotel here, about 20 minutes from Wednesday night’s debate stage. President Obama was 800 miles away, just outside Las Vegas. Both devoted much of the day to practicing for an event that could tip the race for the White House.

The two candidates will face off on the University of Denver campus for the first of three debates. Romney needs to shift the trajectory of the race, and soon; early balloting has already started in some places, and polls show crucial swing states moving in Obama’s direction.