Nick Clegg has just sent out an email to Lib Dem members giving some of the rationale behind the Spending Review. It's very light on detail, but does provide a couple of interesting insights into how the Deputy Prime Minister is seeking to position his party politically going into this afternoon's announcement.

The core argument is, naturally, the same as the one offered by Cameron and Osborne – the outcome of the review is about fairness and, above all, cutting "Labour's deficit". But there are also certain phrases that demonstrate once again how tightly Clegg's fortunes are now tied to those of the coalition's leading Tory figures. The following paragraph is particularly interesting:

The spending review is a thoroughly Coalition product. Liberal Democrat ministers have been involved every step of the way. Our values and priorities are written through the review, like the message in a stick of rock.

As my colleagues Mehdi Hasan and James Macintyre pointed out [2] in the run-up to the Lib Dem conference, the spending review is just the first in a series of tests for the Lib Dems as a party of government, perhaps the most significant being the local elections to come next May. But with the polling numbers [3] long suggesting we can expect a big swell of unpopularity for this afternoon's announcement, the Spending Review isn't without its challenges for the Lib Dems. Members, and a fair number of Lib Dem MPs, will be feeling very uncomfortable this afternoon.

However, the key paragraph of the letter comes at the end, where Clegg lays out his version of the motivation behind the cuts:

We are not taking the decisions today because they are easy or because we want to see a smaller state, we are taking them because they are right.

He said something similar [4] in his conference speech – it's clearly a line designed for the membership, many of whom will be feeling uneasy about the Tories' mantra of "smaller state, bigger society" [5]. Now that Clegg has positioned his party and his ministers so centrally to the Spending Review, it will be fascinating to see how his backbenchers choose to respond, come the inevitable fallout.