Washington is a strange city because, unlike New York, money doesn’t confer status and, unlike Los Angeles, neither does celebrity. The elusive element that structures life and work here is power or the appearance of power. Like electricity, this substance cannot easily be seen. But when it emerges decisively, you feel the atmosphere change in the city. And last week something shifted.

Fourteen senators made a deal. All the president of the United States could do was look on. In a finely balanced Senate, a centrist faction of seven Republicans and seven Democrats shelved the notion of abolishing the judicial filibuster, allowed a vote on three judicial nominees and punted on the others. It was one of those moments when you really understood the founding fathers’ notion of separation of powers.

For a while the Senate — or a free-floating cabal within it — ran the country. The upshot? The president will be mildly constrained in his picks for the Supreme Court later in the year; the Democrats will retain the threat of a filibuster under “extraordinary” circumstances; some judges will be confirmed; and the hard social right is livid. In the same week the evangelical lobby also suffered a defeat on stem cell research, as 50 Republicans defected in the house and voted against the president in favour of federal funding.

But there’s another upshot: John McCain. Called last week the McCain Mutiny, he is a crusty, temper-prone, old-school Republican from Arizona. He’s also a genuine Vietnam war hero who endured five years of torture at the hands of the Vietcong, refusing to be released ahead of any of his comrades. He’s the most popular Republican in the country, one of the least popular senators among his colleagues and would have beaten Al Gore for the presidency in 2000 by a large margin.

That year, as he ran for the Republican nomination, he was ambushed by the religious right in the South Carolina primary, as they put their support behind George W Bush. McCain lost, and when 9/11 transformed George W Bush into a war leader it seemed as if this ageing giant was headed for a cantankerous canter towards retirement.

But times change. After one last blistering assault on the religious right in 2000, McCain made two smart decisions. He refused to countenance running as an independent and he spurned John Kerry’s offer to become a vice-presidential nominee for the Democrats in 2004. He decided instead to be a Republican loyalist.

No, McCain didn’t remove his brain or his conscience. He differed with Bush on campaign finance reform, the management of post-war Iraq and on global warming. But he remained a loyal trooper, campaigning for Bush last year, endorsing him at the New York convention and calming some of his public rhetoric against his Republican rivals.

Most McCain observers saw this as part of his character. For all the liberal fantasies about him, the truth is he is a conservative. He’s pro-life, deeply committed to low taxes and the war on terror. He has thinly veiled contempt for the European governments that opposed the invasion of Iraq, especially France; and, for good measure, he holds the Senate seat once occupied by the grandaddy of the American conservative movement, Barry Goldwater.

It would have been extremely odd to see him in the upper reaches of the Democratic party. For Republicans who feel alienated by the power of fundamentalist evangelicals in the party, McCain is also a secular saint and they would have felt betrayed by his departure.

Journalists, whom he has cultivated for years, adore him — but largely because he’s a Republican who sometimes sticks it to Republicans. In politics, McCain has been intelligent enough to realise that it’s dumb to muddle your brand.

But after last week, the party loyalty begins to seem part of a political calculation as well. Perhaps the most important fact about the looming political climate in Washington, after all, is that for the first time in many years, the president has no obvious heir. His vice-president has said he has no interest in succeeding him. Moreover, the faction most fully behind the current president — the evangelical right — hasn’t managed to come up with any attractive candidate to succeed him. Jeb Bush is regarded as one dynastic step too far. Arnold Schwarzenegger is constitutionally barred. Rudolph Giuliani, the hero of 9/11, may have too much baggage. The dark horses — Virginia governor George Allen springs to mind — have yet to emerge. Why not McCain? The usual answer is: he’s too old and not in good enough health. He’ll be 72 in 2008 and had a recent, nasty bout of skin cancer. But his energy is still prodigious; he has that permanent, nerve-jangling haste that besets those who have been campaigning much of their lives. The media would do anything to help him and, last week, The New Yorker obliged with a fawning profile by Connie Bruck. Other journalists were having the vapours last week over his new clout.

Margaret Carlson of the Los Angeles Times gushed that McCain had “pulled the Senate back from Armageddon”. And Carlson is a liberal Democrat. You begin to see why a poll last year predicted that if McCain had been Kerry’s running mate, they would have beaten Bush by 14 points.

For my part, count me sceptical. It’s not that I wouldn’t want McCain to be president. It’s that his new clout has more to do with the fact that the Republicans have been over-reaching and less to do with his building a base for the nomination. Ending the filibuster was a real stretch and gave McCain and his more moderate Republican allies the opening they needed.

Without the leadership’s errors, McCain would still be on the sidelines. Moreover, the primary system in the Republican party is still strongly tilted toward fundamentalist Christians, and their leadership despises McCain.

But we can dream, can’t we? As George W Bush faces becalming waters, his power is ebbing. That’s the price for sticking with Dick Cheney and having no successor to keep the troops in line.

In Washington, power is never destroyed; it’s merely transferred. Last week was the first obvious shift away from the White House. It may one day be looked back on as the first of many.