MILBANK: First Lady market shopping leaves 'carbon footprint of several tons'...

Let's say you're preparing dinner and you realize with dismay that you don't have any certified organic Tuscan kale. What to do?

Here's how Michelle Obama handled this very predicament Thursday afternoon:

The Secret Service and the D.C. police brought in three dozen vehicles and shut down H Street, Vermont Avenue, two lanes of I Street and an entrance to the McPherson Square Metro station. They swept the area, in front of the Department of Veterans Affairs, with bomb-sniffing dogs and installed magnetometers in the middle of the street, put up barricades to keep pedestrians out, and took positions with binoculars atop trucks. Though the produce stand was only a block or so from the White House, the first lady hopped into her armored limousine and pulled into the market amid the wail of sirens.

Then, and only then, could Obama purchase her leafy greens. "Now it's time to buy some food," she told several hundred people who came to watch. "Let's shop!"

Cowbells were rung. Somebody put a lei of marigolds around Obama's neck. The first lady picked up a straw basket and headed for the "Farm at Sunnyside" tent, where she loaded up with organic Asian pears, cherry tomatoes, multicolored potatoes, free-range eggs and, yes, two bunches of Tuscan kale. She left the produce with an aide, who paid the cashier as Obama made her way back to the limousine.

There's nothing like the simple pleasures of a farm stand to return us to our agrarian roots.

The first lady had encouraged Freshfarm Markets, the group that runs popular farmers markets in Dupont Circle and elsewhere, to set up near the White House, and she helped get the approvals to shut down Vermont Avenue during rush hour on Thursdays. But the result was quite the opposite of a quaint farmers market. Considering all the logistics, each tomato she purchased had a carbon footprint of several tons.

The promotion of organic and locally grown food, though an admirable cause, is a risky one for the Obamas, because there's a fine line between promoting healthful eating and sounding like a snob. The president, when he was a candidate in 2007, got in trouble in Iowa when he asked a crowd, "Anybody gone into Whole Foods lately and see what they charge for arugula?" Iowans didn't have a Whole Foods.

For that reason, it's probably just as well that the first lady didn't stop by the Endless Summer Harvest tent yesterday. The Virginia farm had a sign offering "tender baby arugula" -- hydroponically grown, pesticide free -- and $5 for four ounces, which is $20 a pound.

Obama, in her brief speech to the vendors and patrons, handled the affordability issue by pointing out that people who pay with food stamps would get double the coupon value at the market. Even then, though, it's hard to imagine somebody using food stamps to buy what the market offered: $19 bison steak from Gunpowder Bison, organic dandelion greens for $12 per pound from Blueberry Hill Vegetables, the Piedmont Reserve cheese from Everson Dairy at $29 a pound. Rounding out the potential shopping cart: $4 for a piece of "walnut dacquoise" from the Praline Bakery, $9 for a jumbo crab cake at Chris's Marketplace, $8 for a loaf of cranberry-walnut bread and $32 for a bolt of yarn.

The first lady said the market would particularly appeal to federal employees in nearby buildings to "pick up some good stuff for dinner." Yet even they might think twice about spending $3 for a pint of potatoes when potatoes are on sale for 40 cents a pound at Giant. They could get nearly five dozen eggs at Giant for the $5 Obama spent for her dozen.

But whatever the socioeconomics, there can be no doubt that Obama brought some serious attention to her cause. Hundreds of people crowded the market entrance on I Street as police directed pedestrians to alternative subway entrances. Hundreds braved a light rain and gave a hearty cheer when Obama and her entourage took the stage. "I can't imagine there's been a day in the history of our country when people have been more excited about farmers markets," Mayor Adrian Fenty, Obama's warm-up act, told the crowd.

The first lady, in gray slacks and blue sweater, marveled that the people were "so pumped up" despite the rain. "I have never seen so many people so excited about fruits and vegetables!" she said. (Must be the tender baby arugula.)

She spoke of the global reach of her cause: "The first thing world leaders, prime ministers, kings, queens ask me about is the White House garden. And then they ask about Bo."

She spoke of the fuel fed to the world's most powerful man: "I've learned that when my family eats fresh food, healthy food, that it really affects how we feel, how we get through the day . . . whether there's a Cabinet meeting or whether we're just walking the dog."

And she spoke of her own culinary efforts: "There are times when putting together a healthy meal is harder than you might imagine."

Particularly when it involves a soundstage, an interpreter for the deaf, three TV satellite trucks and the closing of part of downtown Washington