Last week, in a rare sign that wise counsel can still prevail over political expediency, Mervyn King was reappointed Governor of the Bank of England. Unpleasant noises had been emerging from Downing Street as his reappointment was being considered over the past few months, but Mr King's evident mis-steps in the Northern Rock affair should never have been enough to counterbalance the remarkable contribution he has made to the performance of the British economy in the past decade.

As deputy governor and then as Governor, Mr King led the Bank through the first decade of its monetary policy independence. It was especially encouraging that in these difficult political circumstances for the Prime Minister and Chancellor, and at a time when central bank independence is not quite as popular as it was a few years ago, that they bit the bullet and reappointed him.

In the United States, as Mr King was celebrating a new lease, Ben Bernanke, his counterpart at the Federal Reserve, was marking the halfway point in his first term as Chairman. Mr Bernanke, a moderate Republican, was appointed to the job by President Bush and took office on February 1, 2006. His term expires in two years, but his prospects of getting another may be considerably dimmer than Mr King's.

Like Mr King, Mr Bernanke has come in for some stinging criticism in the past few months. The Wall Street crowd thinks that he has been “behind the curve” in cutting interest rates. Inflation hawks think that he is to blame for the weak dollar and rising prices. A growing number of critics point to his role as a Fed governor in the explosion of dodgy mortgage lending in the boom years of the housing market. Even his strongest supporters in the economics profession were baffled by some of his recent decisions, including the emergency 75-basis-point cut in the Fed funds rate two weeks ago.

Unfortunately for Mr Bernanke, Mr Bush will be gone when the time comes to decide whether to reappoint him. Alan Greenspan, his predecessor as chairman, demonstrated such remarkable deftness of political touch that he got himself reappointed by a Republican (President Bush Sr) then twice by a Democrat (President Clinton), then by another Republican (Mr Bush Jr).

It is unlikely that Mr Bernanke - more diffident, much less well politically connected than Mr Greenspan - will be able to move quite as smoothly.

His best chance of staying on will be, presumably, if a Republican wins the presidency in November. It now seems more or less certain (and could become just about conclusive after today's Super Tuesday primaries) that John McCain, the Arizona senator, will be the Republican candidate for president.

Mr McCain has not sounded very enthusiastic about Mr Bernanke. In an interview with The New York Times last month, he was asked if he thought Mr Bernanke had handled his job well. “Depending on the depth of this crisis that we're in, we'll find out whether he acted soon enough and whether he acted appropriately enough,” Mr McCain said. “I don't think it's clear yet.”

Mr McCain has surrounded himself with some serious economists. His principal campaign adviser has been Douglas Holtz-Eakin, a quietly effective former senior economist at the White House and on Capitol Hill, has been careful to observe the rule that you don't say anything controversial about Fed policy in an election campaign.

But Mr McCain is also likely to lean heavily on some big hitters, such as Phil Gramm, the former Texas senator and likely Treasury Secretary in a McCain administration, who is a fervent believer in supply-side economics and may not see eye to eye with Mr Bernanke. Another McCain ally is Jack Kemp, a former congressman who has been harshly critical of Fed policy. One of Mr McCain's academic economic advisers is John Taylor, the monetary economist, who literally wrote the book on central banking.

So Mr McCain, who seems sceptical about Mr Bernanke's performance, has no shortage of potential alternatives. And if a Democrat wins in November - which seems most likely - you would have to guess that Mr Bernanke is even less likely to keep his job.

Mr Greenspan was lucky that his job came up for reappointment in 1996 - right at the end of Mr Clinton's first term. Over three years he had a chance to establish a relationship with the new president and helped to convert him to the virtues of fiscal prudence.

By 1996 the American economy was thriving.

The next president will have to decide on Mr Bernanke within about nine months of taking office. There will be no shortage of hungry Democratic alternatives. Roger Altman, a former Treasury official and Wall Street investment banker, is Hillary Clinton's adviser. Larry Summers, former Treasury Secretary, might also still harbour ambitions - though his ignominious departure from Harvard University after his supposedly disparaging remarks about the intellectual abilities of women may have damaged his prospects - especially with Mrs Clinton. In fact, there will be a long line of academic monetary economists, former Fed officials and Wall Street types available should either Mrs Clinton or Barack Obama come calling.

Of course, mostly it will depend on how well Mr Bernanke is seen to perform in the next year or so.

If the US avoids a nasty recession and the Fed's actions these past few months come to look both bold and wise, then he may overcome the odds. If not, he will probably find himself, like millions of his fellow Americans, looking for a new job.

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