But the state was penalised for breaking party rules by holding its contests - or "primaries" - before 5 February.

This means neither the Democratic nor Republican primaries will count for as much as they normally do.

Why did Michigan hold its primary early?

It is one of a number of states that have brought their votes forward, with a view to maximising their influence on the presidential nomination process.

KEY DATES 15 Jan: Michigan primary 19 Jan: Nevada caucuses; South Carolina primary (Rep) 26 Jan: South Carolina primary (Dem) 29 Jan: Florida primary 5 Feb: some 20 states including California, New York, New Jersey Q&A: US primary elections Primary and caucus dates A caucus guide What is a primary?

A spokesman for the Michigan Republican Party said the state wanted to focus politicians' attention on its big issues, such as the automobile industry and jobs.

In 2004, the Michigan Democrats held their vote in early February and the Republicans in May. In 2000, the Republicans voted in late February and the Democrats in March - by which time the Democratic nomination had already been effectively decided (in favour of Al Gore).

Why was Michigan penalised for this?

In an attempt to stop the rush to the front of the queue, both the Democratic and Republican National Committees decreed that - with certain exceptions - no primaries should take place before 5 February.

The Democrats have allowed four states to hold contests before this date - Iowa and New Hampshire, because of their traditional first-in-the-nation status, plus Nevada and South Carolina, to increase the geographic and demographic diversity of the early contests.

The Republicans allowed only Iowa and Nevada to hold votes before the cut-off date, because technically, those states' contests are non-binding.

Are any other states being penalised for holding contests before 5 February?

Yes. Both parties are penalising Florida, which holds its primary on 29 January.

The Republican party is also penalising New Hampshire, South Carolina and Wyoming.

How are they being punished?

The Democratic Party is barring all Michigan and Florida delegates from voting for the presidential nominee at the party's national convention in the summer.

The Republican Party is halving the number of delegates from all the rule-breaking states.

The whole point of the primaries is to select the delegates that will vote at the national convention, so the Democratic primaries in Michigan and Florida now have little more than symbolic value.

The Republican primary in Michigan being still of some importance was hotly contested.

Did the Michigan Democratic primary go ahead nonetheless?

Yes, but to show their loyalty to the national party, all of the Democratic presidential candidates agreed not to campaign in the state.

And of the mainstream Democrats, all but Hillary Clinton opted to take their name off the ballot last October, so she was certain of victory.

However, supporters of her main rivals, Barack Obama and John Edwards, had the option of voting "uncommitted". Results showed Mrs Clinton with 55% and "uncommitted" on 40%.

Are Michigan's convention delegates likely to be reinstated?

Local bosses from both parties believe that by the time the conventions come around, the national parties will be keen to avoid a row and will allow Michigan's delegates to take part after all.

This was another reason for supporters of Mrs Clinton's rivals to vote "uncommitted".

If reinstated, uncommitted delegates would be allowed to vote at the convention for candidates whose names are not on the ballot.