(AP Photo/LM Otero)

DALLAS - In just the past few days, she's danced with cheering school kids, chatted with troops, swapped ideas with busy parents and engaged in a friendly cooking competition with stars from the reality television show "Top Chef."

Michelle Obama is on a national tour to promote the second anniversary of her campaign against childhood obesity. The images have been disarming, intriguing and non-political - just the type of thing her husband's re-election campaign can't get enough of.

Five years to the day after Sen. Barack Obama announced he was running for president, Mrs. Obama's travels this week offer fresh evidence of what an outsized role she's assumed in the public eye and how powerful a political asset a first lady can be.

And, make no mistake, Mrs. Obama says she's "incredibly enthusiastic" about making the case for her husband's re-election.

Simply put, "I want him to be my president for another four years," she said in a 40-minute interview Friday with a handful of reporters.

In recent weeks Mrs. Obama has seemingly been everywhere: Doing pushups with Ellen DeGeneres. Serving veggie pizza to Jay Leno. Playing tug-of-war with Jimmy Fallon in the White House. And now making a rare four-state tour - Arkansas, Florida, Iowa and Texas - to mark the two-year-point for her "Let's Move" initiative.

The first lady draws a line between her policy efforts on childhood obesity and her political activities. But such distinctions often are lost on the public.

In an election year, it's all to the good for Barack Obama that his popular wife is travelling the country promoting can't-miss issues like healthy living.

"This is a bit of a two-fer," Mrs. Obama acknowledged in her interview on Friday, "because it's an issue that I care about, and it's an issue that's important to the country. ... I want to make sure that what I do enhances him."

To a more limited extent, Mrs. Obama also fills a more overtly political role by headlining private fundraisers that raise millions for her husband's campaign, reaching out to supporters through conference calls to various states and shooting out periodic emails to campaign backers around the country.

That part of her labours will increase considerably in the months to come.

But the first lady said she's careful to protect her time as "Sasha and Malia's mom."

"My approach to campaigning is, 'This is the time that I have to give to the campaign and whatever you do with that time is up to you, but when it's over, don't even look at me ... No calls. No anything," she said.

For now, the first lady's most visible role is tied to her signature issue of fighting obesity, allowing her to connect with voters on an emotional level and relate to them as a mother who has struggled with some of the same challenges that other families face.

"We're constantly trying to make sure that what we do is on point with what is going on in people's lives," Mrs. Obama told parents this week as she chatted with them over low-calorie plates of chicken and pasta at a restaurant in Fort Worth, Texas. "I mean, at one point I was normal. I went to the grocery store and I did all that."

While the president's favourability ratings and those of Vice-President Joe Biden slipped considerably over their first three years in office, Mrs. Obama's have remained strong.

Barack Obama's favourability rating now stands at 51 per cent, Biden's at 38 per cent. By contrast, 66 per cent of Americans have a favourable opinion of the first lady, about even with her ratings on Inauguration Day, according to the Pew Research Center.

That's about where Laura Bush stood in the fourth year of her husband's first term, and it's considerably higher than Hillary Rodham Clinton's 42 per cent at the start of her husband's fourth year as president.

Mrs. Obama is particularly popular with women and younger Americans, polling shows. And she does well with the moderate and liberal Republicans and independents whom Democrats will try to lure away in the November elections.

There are other ways to measure her appeal: Her Twitter account shot up to more than a half-million followers in less than a month. And her Facebook page has more than 6.6 million "likes."

So far, Mrs. Obama has headlined 32 fundraisers over the past 10 months, including six this year.

She's hauling in millions with a fundraising stump speech that mixes a recitation of administration policy initiatives with a personal sketch of her husband as a man who stays up late after the children are in bed fretting over the concerns of ordinary Americans.

It's the same humanizing role that Mrs. Obama serves regularly in her public appearances, as she mixes public policy with stories about her own family.

As for how she's preparing her daughters for the coming campaign, sure to be hard-fought and bitter at times, Mrs. Obama said her focus is on reassuring the girls that "whatever happens, you guys are going to be good. So don't worry about this, just focus on your world."

Preparing them for a victory or loss, she said, "I just try to play both sides of the scenario and make both sides seem great."