CHARLOTTE, N.C. -- President Obama consoled victims of Hurricane Isaac along the Gulf Coast on Monday and stoked the enthusiasm of union voters in the industrial heartland, blending a hard political sell with a softer show of sympathy on the eve of the Democratic National Convention.

At times like these, "nobody's a Democrat or a Republican, we're all just Americans looking out for one another," the president said after inspecting damage inflicted by the storm and hugging some of its victims. He was flanked by local and state officials of both parties as he spoke.

There was nothing nonpartisan about his earlier appearance in Toledo, Ohio. There, the president said Republican challenger Mitt Romney should be penalized for "unnecessary roughness" on the middle class and accused him in a ringing labor Day speech of backing higher taxes for millions after opposing the 2009 auto industry bailout.

Obama's trip to LaPlace, La., was a televised interlude in the rough and tumble of the political campaign, four days after Romney accepted his party's presidential nomination at the GOP Convention in Tampa, Fla., and three days before the president is nominated by Democratic delegates in Charlotte.

Unlike Obama, Romney made no mention of federal aid in his own trip to Louisiana last Friday showing concern and support.

First lady Michelle Obama was already in the Democratic convention city as her husband spent his day blending the work of president and candidate.

He doesn't arrive in North Carolina until later in the week, after concluding a slow circuit of campaign stops in battleground states and the trip to Louisiana.

In LaPlace, Obama went from yard to yard, shaking hands, embracing residents, sometimes posing for photos they snapped. "I know it's a mess," he said of the damage, "but we're here to help."

He said he had promised local residents "we're going to make sure at the federal level, we are getting on the case very quickly about figuring out what exactly happened here, what can we do to make sure that it doesn't happen again and expediting some of the decisions that may need to be made to ensure that we have the infrastructure in place to protect people's property and to protect people's lives."

The federal government spent more than $10 billion to strengthen the levee system around New Orleans after the devastation of Hurricane Katrina seven years ago.

Obama noted that last week's flooding was in a different region, leaving open the question of what the government might do to prevent a recurrence.

A few hundred miles away in Charlotte, the conversion of the Time Warner Cable Arena into a political convention hall was nearly complete. Democrats convene there on Tuesday.

Nearby, union members staged a Labor Day march through downtown. Though supporting Obama, they also expressed frustration that he and the Democrats chose to hold their convention in a state that bans collective bargaining for teachers and other public employees.

There was disagreement among the ranks of the marchers. "I understand their frustration ... but do they really think they're going to be better off with Romney?" asked Phil Wheeler, 70, a delegate from Connecticut and a retired member of United Auto Workers Local 376 in Hartford.

Democrats chose the state to underscore their determination to contest it in the fall campaign. Obama carried North Carolina by 14,000 votes in 2008, but he faces a tough challenge this time given statewide unemployment of 9.6 percent in the most recent tabulation.

Romney relaxed at his lakeside home in New Hampshire with his family as Obama and running mate Joe Biden sought to motivate union voters to support them in difficult economic times. The Republican challenger took a mid-morning boat ride, pulling up to a dock to fuel up his 29-foot Sea Ray and pick up a jet ski that had been in for repairs.

In a Labor Day statement emailed to reporters before he left his house, the businessman-turned-political candidate said: "For far too many Americans, today is another day of worrying when their next paycheck will come."

Campaigning on Saturday in Cincinnati, Romney had likened Obama to a football coach with a record of 0 and 23 million, a reference to the number of unemployed and underemployed Americans.

Obama rebutted him 48 hours later - and play by play.

"On first down he hikes taxes by nearly $2,000 on the average family with kids in order to pay for massive tax cuts for multimillionaires. ... Sounds like unnecessary roughness to me," he said.

"On second down he calls an audible and undoes reforms that are there to prevent another financial crisis and bank bailout. ...

"And then on third down, he calls for a hail Mary, ending Medicare as we know it by giving seniors a voucher that leaves them to pay any additional cost out of their pockets. But there's a flag on the play: Loss of up to an additional $6,400 a year for the same benefits you get now."

Romney denies that his plan to help the economy and reduce federal deficits will result in higher taxes for the middle class. But he has yet to provide enough detail to refute the claim, and Obama's assertion rests on a study by the non-partisan Tax Policy Center.

As for the auto bailout that he backed and Romney opposed, Obama told the audience, "Three years later, the American auto industry has come roaring back. Nearly 250,000 new jobs."

Obama's new campaign commercial said that under Romney's "a middle class family will pay an average of up to $2,000 more a year taxes, while at the same time giving multimillionaires like himself a $250,000 tax cut."

Aides said it would air in Colorado, Iowa, New Hampshire, Nevada, Ohio and Virginia, the by-now familiar list of battleground states where the 2012 race for the White House is likely to be decided.

The president and aides have acknowledged for weeks that they and the groups supporting them are likely to be outspent by Romney, and recent figures say that has been the case in television advertising in the battleground states for much of the past two months.

Republican strategists contend that they have used the advantage to begin to erode Obama's job favorability ratings, but declined to provide any polling results to support the assertion.

At the same time, reports by firms that track advertising show that Republicans hope to expand the campaign battleground into Wisconsin, Michigan and possibly Pennsylvania and Minnesota. An effective ad campaign there in such states could force Obama to divert resources from other states to defend turf he has long assumed would be his with relative ease.

Republicans ramped up their counter-programming as the opening of the Democrats' convention approached.

"People are not better off than they were four years ago. After another four years of this, who knows what it'll look like then," said Republican vice presidential candidate Paul Ryan, campaigning in Greenville, N.C. "We're not going to let that happen." Obama's top campaign surrogates had flinched from saying on Sunday that the average American is better off than four years ago, but they - and Biden - hastily recalibrated their response overnight.

"You want to know whether we're better off? I've got a little bumper sticker for you: 'Osama bin Laden is dead and General Motors is alive,'" Biden told a campaign crowd in Detroit, the city that for generations has been synonymous with the American auto industry.