Image copyright Getty Images Image caption Sanders speaks politics from the gut

I'd seen Bernie Sanders in person and watched him on television, and frankly I just didn't get it. He seemed grumpy, fed up, irritated, irascible and old. Last night watching the debate, I suddenly got it, I really got it.

Here is a man who speaks politics from the gut. He calls it as he sees it, and there seems to be no filters in what he says. If he has got an idea, he'll express it with clarity.

While other politicians might have sounded rehearsed when taking about Hillary Clinton's "damn emails", Sanders sounded genuinely sick of the subject.

He is way to the left of anything else you'd find in American politics. He wants to bring in healthcare like you have in Europe and social security systems that the United States does not have at the moment. He wants environmental politics that would be an anathema to many in the oil industry. He kept talking about Scandinavia as if he wants to import Scandinavia wholesale. It is like going into IKEA and saying "I'll buy the whole store".

Of course the United States is not Scandinavia. But that won't bother the legions of young people who have been attracted to this brand of honest politics where there are no concerns about whether it makes you electable or unelectable. He seems to have a magic that makes people believe anything is possible.

Clinton has the reverse problem. You feel that everything she says has gone through 30 filters to get out any germs or creases or wrinkles along the way to make it sanitised so that it will stand up to scrutiny.

She's a brilliant debater, but you didn't feel the sense of excitement about her policies as you would about Bernie Sanders. Why is that?

I suspect the thing about Sanders is that he knows that he's setting up policies that will never have to be implemented. Deep down, he and his backers know that he isn't going to win the nomination or keys to 1600 Pennsylvania Avenue.

Image copyright Getty Images Image caption University students are major sources of support for Sanders

Clinton has to have policies that could be put in place the moment she gets to the White House. And so it's careful. It isn't taking you away believing there is a new Jerusalem to be built on the Hill.

Clinton knows that policy changes incrementally and sometimes torturously. That is what she offered in the debate last night.

Intelligent and battle-hardened, she has the policy details down. She knows what it takes to implement policy. But those policies aren't going to make voters believe that a new dawn is being born for America.

In French politics, which I covered for a long time when I was the BBC's Paris correspondent, the presidency is held over two rounds - the first round of voting two weeks before the final round.

It is said in French politics that in the first round you vote with your heart and in the second round you vote with your head.

Image copyright Getty Images Image caption Sanders brings idealism while Clinton is more pragmatic

Well in the equivalent situation of US politics, it seems that in Sanders you're voting with your heart and in Clinton you're voting with your head.

Clinton had a good night last night and she was absolutely on top of every detail. She was funny, passionate and did everything her campaign could have hoped for. All of which makes me wonder if there's little room now for Vice-President Joe Biden in this race.

Biden's calculation is probably based on the fact that Clinton's poll ratings will continue to slide, her backers will continue to have doubts and the base will continue to grow more disenchanted.

I suspect that Clinton did enough to stem that decline last night and maybe, just maybe, she's a step closer to that nomination.