Pittsburgh ? Party’s over. The visiting police and protesters are gone; the fences and barbed wire are coming down. Someone’s making a fortune moving concrete barriers out of town. Regular cars are replacing limousines on the street. We can sell newspapers in metal boxes again. Downtown is no longer Brigadoon on the Monongahela.

But the end of the G-20 (and the end of a hectic week for Barack Obama, who also appeared at the United Nations) means the beginning of the next phase of the Obama presidency. The set-piece speeches and photo ops were nice while they lasted — the diplomatic equivalent, in the words of the old song, of dancing and dreaming through the night — and the effect of it all may well be lasting. The Pittsburgh communique raises a lot of hopes, and raises the stakes for real action on the economic ills that still plague the globe.

Now, however, the real slog begins, and it will surprise you to see how swiftly the grand talk about regulating financial markets and winning global economic stability recedes to the background and the old problems come raging into focus.

Old problems await

The old problems are Iraq and Afghanistan and, if you figure that presidents since Truman have been wrestling with an overhaul of the way we finance medicine, you can add the overhaul of the health care system to the dreary list. It’s enough to make the White House yearn for the difficulties of figuring out which world leaders didn’t want meat served to them at the Phipps Conservatory dinner during the Pittsburgh summit.

The president’s foreign policy approval ratings slipped over the summer and he now stands at the 50 percent mark — not bad of course, as long as you discount the downward trend, which you can’t. The rate of Americans who fear that the nation will invest a lot of lives and money in Afghanistan and have little to show for it is about the same, give or take a single percentage point, as the rate that fears the United States won’t do enough to deal with al-Qaida and the Taliban in Afghanistan and will be more vulnerable as a result. So there is no solace on Afghanistan for the White House in the new Wall Street Journal/NBC News poll.

Not much in there either on health care, where the public is evenly split on creating a public heath care plan administered by Washington to compete with private insurers. The problem here is not so much the 48 percent to 46 percent verdict against a federal plan, which is well within the margin of error. The problem is that the people who want one really, really want one, and the people who don’t want one really, really don’t.

Health care divide

This is as divisive an element of the political landscape as any in recent years. Many of the president’s most ardent supporters believe he promised them a fair shot at the public option. But many of the president’s tentative supporters — the ones who saw him as an unusual figure, or as an inspiring leader, or as an evocative symbol, or even as a vehicle for concluding a painful passage in American history — drifted into his camp with no allegiance to the public option, and perhaps with real skepticism toward it.

Right now there is a lot of brave talk about how the health care imbroglio will end happily, most of it involving the notion, fanciful or not, that before long Sen. Olympia Snowe of Maine will win some concession, meaningful or not, that may legitimize the Senate bill for others in the Republican caucus.

Don’t expect a groundswell of GOP support. Instead you can wager that the struggle between taking significant steps on health care or merely taking preliminary steps on the matter will form the leitmotif of conversation on Capitol Hill for the next several weeks. No matter what he says publicly, that’s not what Sen. Obama had in mind in all those caucus and primary debates.

Urgency on Afghanistan

The decisions on Afghanistan cannot wait for the plodding pace of Congress. Though the president has warned that it is better to make the right decision than to make a swift decision, there remains real urgency in Central Asia, an urgency underlined by the onetime confidential memorandum prepared for the administration by Gen. Stanley A. McChrystal, the senior U.S. commander in Afghanistan. He is calling for an Iraq-like surge in the region, and as a result the White House has undertaken a new review of its policy in Afghanistan.

Here again there are no good or easy choices. The general and the civilians are attempting to minimize the notion that there are rifts between those in uniform and those in mufti, a word you haven’t heard in years but one that, given its Islamic roots, may be primed for a robust comeback. Adding to the agita is the worry that the Taliban is inching back in a number of Afghan provinces, even collecting taxes and conducting legal trials. So much for the notion that the insurgency was petering out.

The president’s decision on removing missiles in two countries (Poland, Czech Republic) helped smooth the way for a third country (Russia) to help isolate a fourth (Iran). That was a controversial decision, but it provided the diplomatic equivalent of a 6-4-3 double play. No such move is available in Afghanistan, where the allies (Pakistan, on some days at least, plus Canada and Britain and some others) are jittery and where the prospects (further Taliban advances, possible terrorist bases) are terrible.

Throw in Iraq, which may never be pacified, and it’s enough to make Obama long for the relative tranquility of Pittsburgh, where the Palm Court and the Serpentine Room, the tree ferns and the cycads, combined on his welcoming dinner to form a beguiling sense of serenity. But the party’s over. (Nat King Cole would go further and add: “The candles flicker and dim …”) The work now begins, and on fronts both domestic and international there is only struggle ahead.