Here, in the big top of American politics, the audience has been amazed — even awestruck — by President Obama’s ability to juggle an ever-growing array of crises and awkward policy initiatives over the past 100 days.

However, anyone who has tried keeping so many balls in the air knows that when you drop one, they all tend to come crashing down.

On Capitol Hill, some Democrats have begun to regard Mr Obama’s dizzying first-year agenda — which includes measures to transform the US financial system, healthcare reform, the revival of state education, the introduction of limits on greenhouse gas emissions and now a battle over who will replace David Souter on the Supreme Court — with trepidation. They fear that they may yet be left to pick up the pieces.

Chris Van Hollen, chairman of the Democratic Congressional Campaign Committee, has publicly voiced doubts about whether Mr Obama is wise to pursue energy legislation so aggressively when objections to the proposed cap-and-trade system on carbon use mean it is unlikely to become law this year. Congressmen from rust-belt and coal-dependent states are already preparing amendments to the Bill.

Even if it survives the House of Representatives, the Senate — where Democratic leaders admit they do not have sufficient votes on this issue — is almost certain to block it.

Mr Van Hollen, keeping a wary eye on mid-term elections next year, asks why vulnerable Democrats are being leant on to back a measure that Republicans are already denouncing as a tax on American jobs. Instead, he argues, climate change should make way for what ought to be the top priority this year: healthcare reform.

There have been some ugly spats on this issue, not only involving Mr Van Hollen but also between Henry Waxman and the man he usurped this year as chairman of the House of Representatives Energy Committee, John Dingell.

On Tuesday, Mr Obama intervened in this gathering dispute by calling almost three dozen Democrats to the White House to urge unity on climate change. “Once in a while when you’re a member of Congress you do something that really matters,” he told them.

Mr Waxman said later that he planned to press ahead with the Bill and get it moving in his committee by the end of the month.

The White House believes that even if the Senate votes the Bill down, it is important to show willing ahead of negotiations in Copenhagen this December, when world leaders hope to agree a successor to the Kyoto Protocol.

Such a route is fraught with danger. Inviting defeat on this issue now could make it harder to get legislation through at a later date. The Waxman Bill — criticised abroad for not going far enough — risks rallying a demoralised Republican party and dividing Democrats. There is even a danger that congressional overload could threaten other key legislation, including healthcare.

Mr Obama, however, appears determined to drive forward now at a time in his presidency when he has maximum opportunity to make progress. Politically, he bestrides the Earth. Some of his supporters believe he can walk on water. For the President’s next act we will see how he copes with the hot air of a warming planet.

Times Recommends

• It’s only Brits who don’t appreciate me, says Blair
• Party’s over for Greek graspers
• White House tightens security for Xmas marathon