BACK in February of 2009, newly-inaugurated President Barack Obama's Council of Economic Advisers explained the somewhat rosy economic forecasts underlying the adminstration's budget by writing:

[A] key fact is that recessions are followed by rebounds. Indeed, if periods of lower-than-normal growth were not followed by periods of higher-than-normal growth, the unemployment rate would never return to normal.

Greg Mankiw challenged this argument and had a bit of an argument over the question with Paul Krugman. The issue was whether there was a "unit root" to output or not, that is, whether an unexpected decline in output was likely to have a large permanent component or not. Mr Mankiw said at the time:

On the substantive question that Paul raises about the unit root literature and the distinction between cyclical and other fluctuations in output, it is an issue that Campbell and I addressed in a companion paper, where we decided that the conventional wisdom on this matter, which Paul still espouses, does not hold. I do not claim we had the last word on the subject, but it is just wrong to say we missed the obvious point that Paul raises. I don't blame Paul for not being aware of this paper. After all, he is an international trade theorist rather than an empirical macroeconomist, and it is hard for anyone to stay informed about all literatures in the field.

Now as it turned out, Mr Mankiw was right to be sceptical; growth has been more sluggish than the administration predicted. The Obama administration has since taken to citing the evidence presented by, for example, Carmen Reinhart and Vincent Reinhart, which suggests that recoveries after debt crises are often slow.

You can see where this is going. On Sunday, Mitt Romney mused on the state of the economy:

“That is what happens in a normal process,” he said. “When you come out of the kind of recession we’ve had, you should see this kind of creation. We should be seeing 200-, 300-, 400,000 jobs a month to regain much of what has been lost. That is what normally happens after a recession, but under this president we have not seen that kind of pattern."

The argument behind Mr Romney's point was laid out in a new white paper authored by the campaign's chief economic advisers including...Greg Mankiw. The economic fig leaf for the reversal in position seems to be a citation of this new economic paper by Michael Bordo and Joseph Haubrich. It concludes that a deeper recession will typically be followed by a stronger recovery, BUT the last three recoveries seem to have been different, and housing weakness appears to explain a lot of the weakness of the present recovery. The Romney white paper offers vague criticisms of the Obama administration's approach to housing. It offers no alternative policy, however, and another of the white paper's authors—economist Glenn Hubbard—has expressed enthusiasm for elements of the Obama housing approach.

Of course, the campaigns must work very hard to pretend that presidential policy choices matter a great deal relative to, say, the actions of the Federal Reserve. And so there is much talking around the fact that perhaps ultimate responsiblity for the shape of the recovery should rest with Ben Bernanke (who was, to be fair, reappointed by Mr Obama). As Andy Harless points out, nominal output also, and disconcertingly, has appeared to have a unit root in this recovery.

You may be unsurprised to learn that there has been a considerable evolution in thinking within the Romney camp on monetary policy. In 2009, Mr Mankiw was calling for higher inflation; he's now linking to pieces arguing that inflation is a worrying risk. In 2010, he called QE2 a "step in the right direction". A year later, he was quoting Chicago economist John Cochrane, writing that QE was a distraction from the need to deal with the "microeconomic, tax, and regulatory barriers to growth". Fittingly, Mr Romney came out in opposition to new QE in his Sunday comments.

If he's elected, I suspect his view on the merits of new monetary expansion will change again, and rapidly. When it comes to economics and politics, people are often capable of "a staggering level of open-mindedness".