"There's a reason he's in eastern Iowa," said Ben Lange, a Republican challenging Democratic Iowa Rep. Bruce Braley. Lange appeared with Romney on the boat in Dubuque.
Obama lost white, non-college-educated voters to Republican John McCain in 2008, according to exit polls. These voters made up nearly half of all Midwestern voters, more than any other region. Obama had support from 46 percent of these voters in the Midwest, compared to McCain's 52 percent. Nationally, the group split 40 percent for Obama, 48 percent for McCain.
Recent polling by Associated Press-GfK suggests Obama is underperforming his 2008 showing in this group. In a May survey, just 31 percent of white non-college-educated adults in the Midwest said they backed Obama, compared with 57 percent who said they supported Romney. The May poll showed Obama faring better nationally, but still trailing Romney 38 percent to 53 percent.
Democrats argued that the president's support, for instance, for the 2009 auto industry bailout, which Romney opposed, demonstrates better understanding for working-class voters.
"President Obama will win in the upper Midwest because he stands for the basic Midwestern values of hard work, fair play and a level playing field," said R.T. Rybak, vice chairman of the Democratic National Committee.
The population in Democratic-controlled Detroit has fallen sharply, by 25 percent in the last decade, and Detroit's Democratic voter turnout operation has also eroded some due to political struggles of the party-controlled mayor's and Wayne County executive's offices. The problems "really put a strain on the Democratic infrastructure," said Stu Sandler, former Michigan Republican Party executive director.
Romney is sure to face continued criticism by Obama and his allies for opposing the automotive industry bailout, which the president credits with saving Detroit and buoying car-related manufacturing in nearby Ohio.
In Pennsylvania, Romney toured Weatherly Casting and Machine Co., a century-old foundry marked by rusted steel beams staffed by union workers.
Turnout in these small manufacturing towns will decide how competitive Romney will be against Obama in Pennsylvania. But even Democrats acknowledge the fight might be tougher than it appears, considering no Republican has won here since 1984.
"It's going to be a close race in Pennsylvania," said former Rep. Patrick Murphy, a Democrat from suburban Philadelphia.
Romney took a different tack in Ohio, which is dominated by large regional metro areas more so than the other states on the tour.
Instead of focusing just on small towns and cities, Romney's Ohio leg of the tour took him to areas just outside major metro areas of Cleveland and Columbus.
"Because they have so many big cities, they have so many suburbs," and fewer working-class voters, said Katie Gage, Romney's deputy campaign manager.
Beaumont reported from Des Moines, Iowa.