Fred Thompson's decision to consider a run tells us more about the weakness of the Republican field than it does about his strengths. The fact that he would enter such an expensive race at this stage is just more proof - if it were needed - that the party has yet to produce a viable presidential contender.

With no one candidate attracting more than 25% of the party's support and almost two-thirds of Republicans unsatisfied with their choice on offer, Thompson at the very least offers more choice.

The relief at his likely entrance, however, is likely to be short-lived. While he is clearly a consummate performer his down-home manner is liable to grate with a wider electorate that has just about had its fill of folksy straight-talkers. As my colleague Michael Tomasky pointed out earlier in the week, he's no Reagan. Bereft of ideas, an agenda or decent candidates, saddled with a unpopular war they started but can't finish and a base that is energetic and enervating to moderates in equal measure, the Republicans do not have anything to rally around. At this stage there is only one thing that could possibly save them - Hillary Clinton.

Clinton remains the Democratic frontrunner with a volatile but consistent lead. She has more money, name recognition and high-level endorsements than any other candidate. Moreover in a straight run-off with the other Republican challengers polls suggest she would win. So what's the problem?

She is the only Democratic candidate that could seriously motivate people to vote Republican. Her favourability ratings are three times lower than her main challenger, Barack Obama. In short, no one can get Republicans to the polls like Hillary can. Not because they love whoever she would be standing against, but just because they will be standing against her.

Now, there are at least three good reasons why one might decide to simply bite your lip and push ahead anyway.

First, as irregulartimes.com points out, much of this animus is motivated by misogyny. Asked to pick out words that best describe her back in 2003, people chose "intelligent" and "smart". The third word, pollsters at the Pew Research Centre said, is a pejorative term that "rhymes with rich".

Second it would be great to have a woman president.

Third, Bush was a polarising figure - was there anyone out there who really voted for Kerry as opposed to against Bush? - but he still won.

The first count is straightforward. Misogyny is wrong and progressive people must fight it where they find it.

The second is tricky. It would be great to have a woman president. Hell it would be great to have a black woman president. But if Condi were standing I wouldn't be voting for her. And Margaret Thatcher didn't do a great deal for women either. It's not the gender or the race of the person that makes them progressive - it's their agenda.

Which brings us on to the third point. The reason Bush won was because for everyone who loathed him there was a little bit more than one who loved him. With his gay-bashing and war-mongering he motivated and could therefore mobilise his base. Clinton can't. She backed the war and has been an opportunist on issues ranging from flagburning to abortion. Nominating her would be a double-whammy. The right would be reinvigorated while the left would remain marginalised.