I believe it is unrealistic of Mr Cameron to claim he will obtain a renegotiation of the terms of Britain's membership in the E.U. It is as Nick Clegg said in a recently published BBC article (which I will link at the bottom). The outcome of Mr Cameron will either be "symbolic" and not particularly significant as he may be able to renegotiate minor environmental laws etc...that would apply to Britain. Or, he will have to fight for major changes in Britain's membership, changes that will effectively disadvantage the rest of the E.U in comparison to Britain. The UK would be in a "one foot in, one foot out" position, which is not what the E.U is about. It is the E.U's demanding membership criteria that has made it the relatively secure region in the world it is now. And I feel that Mr Cameron's initiative is undermining that.
He may be able to secure the British people's support, if he is elected by an overwhelming majority of Conservatives, who are perhaps the most Euro-sceptic party in the UK.
The BBC article: http://www.bbc.co.uk/news/uk-politics-21177614