And he added: "You can't make it happen if you write off half the nation before you take office."
Romney was showing signs of picking up his pace.
He scheduled a blizzard of interviews with ABC, CBS and NBC, his second round of broadcast network appearances in three days after weeks of ignoring their requests. He also did interviews Tuesday with Fox News and CNN.
The new Romney TV ad, at 60 seconds, is a longer and softer approach in which he speaks about people struggling to pay for food and gas with falling incomes.
At one point on Wednesday, the two candidates spoke from different sections of northern Ohio at the same time, their scenery as different as their message.
At a factory in Bedford Heights, Romney appeared on a stage surrounded by visual evidence of Ohio's manufacturing base - giant coils of steel wire, metal beams, yellow "caution" signs - and spoke as machines whirred in the background. He appeared with Mike Rowe, an everyman TV personality and pitchman.
Obama appeared at two packed college basketball arenas, delivering his message first to a boisterous crowd of more than 5,000 at Bowling Green State University and then to 6,000 screaming supporters at Kent State University.
He said a student who introduced him broke his wrist during a game of ultimate Frisbee. Exhorting the crowd to vote, he said, "You got to play through injuries."
The campaigns tried, too, for footholds on other fronts.
Both sides kept up their attempts to paint each other as weak in dealing with China, efforts aimed at wooing support from working-class voters whose jobs might suffer from imports from China.
The Romney campaign has started setting up flat-screen TV monitors at its events to screen a video about his personal and business story. It was first aired at the Republican National Convention as a way to introduce him to America but went unseen by most viewers because it did not run during prime-time coverage.