A few thoughts on how to handle the world's most potent political weapon

Dear Mr President-Elect,

I thought I'd try to get in early and drop you a line. I'm sure you know of the tradition in which an outgoing president leaves a handwritten and confidential letter to his successor, tucked into a draw in the Oval Office, setting out what he learned in the job – and warning of the pitfalls ahead. Well, you'll have to wait three months, till your inauguration on January 20, for that testament of wisdom from George W Bush. So in the interim I thought I'd take the liberty of offering a few thoughts as you transition into the most powerful job in the world.

First, I should explain that I'm not certain who you are: as I write, Americans are still lining up in their millions, waiting to cast their votes. I don't yet know the result, though I have the same strong hunch as everyone else. I'll be working on that assumption (though offering a few alternative observations in case that's wrong).

Your most immediate task will be to heal the rift left by this extraordinary election. President Obama – if it is you – you will face a small rump of the electorate that refuses to accept your legitimacy. Among a bigoted hardcore, this will be about race. You may have seen the YouTube footage of supporters at a McCain rally in Pottsville, Pennsylvania, last month, openly telling the camera that a black man did not belong in the White House.

But this sentiment will extend beyond the racists. Just look at what happened to Bill Clinton, dogged for eight years by an organised right wing who deemed him unfit for office from the very start. I attended some of those final Republican rallies, and you wouldn't like what the folks in the crowd said about you: that you were buying the election with mysterious donations, probably from America's enemies. Bonkers, no doubt – but just the kind of wild theories they used to spread about Clinton. (If President McCain is reading this, you'll have problems too: starting with the colossal wave of anger and disappointment your surprise victory will have unleashed.)

But if your opponents present a problem, your supporters do too. President Obama, you carry on your shoulders the most enormous expectations. The mere fact of your election as America's first black president is historic, but many, many millions – in the US and around the world – expect you to be a "transformational" leader. It is a word you used yourself during the primaries, when you contrasted the impact of Bill Clinton unfavourably with that of Ronald Reagan, and it is the word Colin Powell used about you. People don't simply expect you to mind the store for the next four years. They expect you to be a Franklin Roosevelt for the 21st century.

So you'll need to manage expectations, explaining that even though you have healthy Democratic majorities in the House and Senate, that doesn't mean you can always get everything done. You can point to both Clinton and Jimmy Carter as unhappy precedents. (President McCain, here you have the advantage of low expectations: saddled with a hostile Congress, you'll get credit for getting anything done at all.)

Still, you arrive with that most powerful of political weapons: a fresh mandate. To maximise that power, you need to act fast. It's a cliché to invoke FDR's Hundred Days, but that's a cliché for a reason: it is in those first three months that the president's muscle is strongest. The momentum of an election victory compels Congress to cooperate — witness Reagan's 1981 tax cuts. Delay, and you'll get bogged down — look what happened to Clinton's healthcare plan. Absurd as it seems, by late 2010 the first stirrings of the 2012 election will be under way: you will be focusing on winning a second term. So move quickly.

In what direction? President Obama, CNN asked you late last week to rank your priorities, and you rightly stated that, first, you would have to repair "the plumbing" of the financial system that visibly came apart in September. There is an irony here. The same event that gave you such help in the campaign – after the economic collapse, you never lost your lead in the polls – will give you a huge headache in government.

And now it will be your responsibility. When President Bush went on TV to calm the markets – only to see them slide further – that only damaged the Republicans and boosted you. But this is your problem now. If you address the nation and the markets still plunge, it will be your prestige that is dimmed.

Let's assume you achieve the financial stability without which nothing else is possible. What next? In that same interview, you ranked energy independence as your very next priority – ahead even of the old Democratic shibboleth, universal healthcare. That makes good sense. For, as you argued in the final weeks of the campaign, a recession is exactly the moment to carry on spending, in order to maintain demand. (President McCain, you'll need to quietly ditch your promise of a spending freeze.) But if the government is going to shell out billions of dollars, it ought to be on a project that needs to get done anyway, something that will last.

No mission fits that bill better than the transformation of the way America generates and uses energy. To address the former, you need to construct a congressional coalition that would radically alter the market in electricity, giving power companies every incentive to use what one analyst calls "fuels from heaven" – chiefly wind and solar – rather than "fuels from hell," such as oil, coal and gas, that have to be extracted from the earth. For the latter, you'll have to lead a massive effort to reduce energy consumption, retooling everything from car engines to loft insulation.

It will be an enormous task, on the same scale, if not greater, than anything achieved under the New Deal. But the benefit could be enormous, creating jobs, keeping the economy afloat, finally reducing America's mammoth carbon emissions – and weaning the US off its dependence on oil imported from the world's most unstable regions. Such a mission would probably consume your entire presidency. And yet, if you succeed, you will have assured your reputation for generations. (President McCain, you could make history here too – though you may need to have a word with Vice-President Palin, on record as denying any human involvement in climate change.)

On the international stage, President Obama, you have a rare opportunity; you have excited hopes around the planet like no president since John F Kennedy. Yes, that gives you another expectation-management problem: act like anything less than a global messiah, and they'll cry betrayal.

But it also hands you a great strength in international affairs. When you visit fellow world leaders, you'll have great leverage: domestic public opinion in those countries may well prefer you to their own leaders. If you demand something – say coordinated action on climate change – your fellow heads of government will be under pressure to give it. At least in the beginning.

Of course, your intray is bulging. You have promised to prevent a nuclear Iran, end the war in Iraq, crush al-Qaida in Afghanistan and Pakistan, and work to reconcile Israelis and Palestinians. That's quite a set of commitments.

And of course, you're now feeling exhausted and elated. Congratulations, Mr President: you have worked so hard to reach this day. But the real work has not even begun.

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