What?

The Clinton campaign has suggested the idea of a 'dream ticket', with Senator Obama running as Senator Clinton's running mate, probably as vice-president. Senator Obama has rejected the idea.

When?

The Democratic National Convention, where the Democratic candidate will be officially chosen before the presidential elections in November.

Where?

So far, Senator Obama has won support in 25 states compared to Senator Clinton's 16. There are elections in nine more states to go.

Why?

Why has Senator Obama dismissed the idea of running with Senator Clinton? Firstly, as he is currently in the lead in terms of delegates won, he said: 'I don't know how somebody who is in second place is offering the vice presidency to somebody who is in first place.'

Secondly, having been accused by the Clinton camp of lacking foreign policy experience, he asked: 'If I'm not ready, how is it that you think I would be such a great vice-president?'

How?

How does Senator Clinton's team feel about the idea? By joining forces, the two hugely popular candidates would be hugely likely to beat Republican John McCain. As former president Bill Clinton says, they 'would be an almost unstoppable force'.