During the coalition talks and after the general election in May, Vince Cable addressed a meeting of Liberal Democrats and told them that "my heart beats on the left". What he meant, of course, was that he was closer to Labour than to the Conservatives, even to David Cameron's liberal Conservatives.

He was still then just about the nation's favourite Vince, a self-styled "free radical" and economics sage. All the same, he urged his fellow MPs to follow him into coalition with the Tories, because, as he told me when I interviewed him in September at a fringe event at the Liberal Democrats' conference in Liverpool, he was "an enthusiastic deficit hawk", and believed that the deficit had to be cut faster and harder than Labour proposed, with some "in-year cuts". He also spoke to me about the pressures of collective responsibility.

Now, all these months later, it's clear just how damaged the Lib Dems have been by their association with the Tories. They are as low as 8 per cent in some polls. Effigies of their leader, Nick Clegg, have been burned on the streets. Students are rioting because of "betrayals" and broken pledges on tuition fees. They are perceived as flip-floppers and liars.

As ever, the truth is more complicated. I had dinner recently with a senior Lib Dem minister who explained just how much his party was doing inside government to "rein in and moderate" the Tories.

Cable is a social democrat and a Keynesian economist by training. He once told me over lunch at the New Statesman that, though he left the Labour Party long ago, he believes "passionately in the redistribution of wealth".

This week, as we all know, "Saint Vince" was humiliated after he was secretly recorded by those two giggly female undercover reporters at his constituency office; he has since been stripped of key responsibilities as Business Secretary after his assault on his "enemy", Rupert Murdoch.

His disparagers, perhaps long jealous of his popularity, have delighted in his humiliation. They have lined up to insult and traduce him. Newspaper columnists, from all sides, have been leading the charge. He is finished, they say. He is arrogant and complacent.

When the revelations broke, Ed Miliband called on David Cameron to sack Cable. This was a mistake by the Labour leader, because one day soon he may well need Cable's support. Instead of calling for him to go, he should have concentrated on the substance of what he'd said. Miliband was in front of an open goal and missed the target. Only the next day did he firm up his attack on the coalition.

Yet Cable had confirmed what many of us suspected – that this coalition is no "love-in". The Tories are in charge and they are behaving recklessly. The Lib Dems are taking the heat and they are being burned. In their haste to overturn Labour's legacies and dismantle Gordon Brown's client state, the Tories are in too much of a hurry – the admirable Tim Montgomerie, of Conservative Home, has written in the New Statesman of the "breakneck coalition". Their reforms to the health service, the welfare system and education are zealous and dangerous. Indeed, as Cable said, "they have not been thought through", as Michael Gove demonstrated once again with his latest reversal, this time on the School Sport Partnership programme (cut one minute, restored the next!).

Vince Cable may be something of a lone wolf, but he remains hugely popular among activists, as I discovered at that fringe meeting in Liverpool. Later, at the same conference, on 22 September, he gave a good speech in which argued for a new approach to taxation, switching the burden from earned to unearned income, from taxing income, or jobs, to assets, principally property and land. He said:

It will be said that in a world of internationally mobile capital and people it is counterproductive to tax personal income and corporate profit to uncompetitive levels. That is right. But a progressive alternative is to shift the tax base to property, and land, which cannot run away, [and] represents in Britain an extreme concentration of wealth.

(I wrote about the need for land reform and a new social democratic model in the New Statesman cover story of 18 October.)

Cable's mistake was to trust those two crafty female reporters not wisely, but too well. We demand that our politicians tell the truth but then vilify them when they speak candidly to "constituents". He's guilty of nothing more than vanity. It is correct that he remains in the cabinet, even though he is for now diminished.

Footnote: By the way, Vince sure knows how to wear a hat. He's been a fan of the fedora for years, and was wearing a particularly rakish one in photos taken after his unfortunate gaffe. Unkind observers might say it made him look like a minor character in a 1950s spy thriller. But everyone else will just be glad it's not a William Hague-style baseball cap.

Incidentally, can you imagine Cameron or Osborne in a hat? Beanie – too student protest. Flat cap – too Labour. Bowlers, boaters or top hats – too Bullingdon Club. That just leaves a Stetson . . .