This race seems to be going on for ever. What stage has it reached?

Today’s primaries in Indiana and North Carolina will be the 49th and 50th contest in the battle between Hillary Clinton and Barack Obama for the Democratic nomination. It is still Mr Obama’s to lose. To win, a candidate needs 2,025 delegates. Mr Obama has 1,739; Mrs Clinton 1,608. It is an almost insurmountable lead.

Yet neither will win enough elected delegates to clinch the nomination. If, as is likely, they roughly split the remaining 404 pledged delegates on offer in the remaining eight contests (including the 187 up for grabs tomorrow), then Mr Obama will have won more elected delegates, but will fall short. The nomination will be decided by the Democratic Party’s 795 super-delegates: the congressmen, senators, former presidents, governors and senior officials who can back either candidate.

So far only 277 super-delegates remain undeclared. Mrs Clinton has 269; Mr Obama 249 — yet since February 10 he has gained a net total of 121 super-delegates to just 45 for her. If the remaining elected delegates are roughly divided, the former First Lady will need to persuade three quarters of the undeclared super-delegates to support her. It is a very tall order.

Then why are Indiana and North Carolina important?

Mr Obama has the maths on his side, Mrs Clinton has the momentum. The Illinois senator has not won a primary for eight weeks (he won Guam’s tiny caucuses by seven votes on Saturday). He has lost all the recent big state contests to Mrs Clinton — Texas, Ohio and Pennsylvania. He has suffered his worst month of the campaign, with the controversy over his former pastor and his remarks that small-town Americans cling to guns and religion. Mrs Clinton has won overwhelmingly among white, blue-collar voters, a crucial constituency in the general election.

Mrs Clinton has to win Indiana to keep her candidacy viable. Polls show her about six points up. Mr Obama badly needs a victory to stop the rot and steady the nerves of super-delegates. Yet his 23-point lead in North Carolina has been cut to single digits. If he loses badly in Indiana, and among white voters, it will bolster Mrs Clinton’s argument that he is a general election liability.

What happens next?

If Mrs Clinton loses both, super- delegates will likely stampede towards Mr Obama and her campaign will be doomed. If she wins both, it will turn the race on its head. If she wins Indiana and he wins North Carolina they will grind on to the final contests in Montana and South Dakota on June 3.

Why is Mrs Clinton still fighting?

She sincerely believes that she is the better candidate and more able to beat John McCain in November. She has won far more big general election battleground states. She still believes she can win. She has started enjoying herself. Pundits are praising her grit — or as one union boss said, her “testicular fortitude”. And the Clintons never give up. Ever.

Who is most likely to be president — Clinton, Obama or McCain?

By every metric this should be a disastrous year for the Republican candidate. Voters want the Democrats back in the White House. But in head-to-head match-ups, Mr McCain is running even with both Democrats. Whoever wins the Democratic nomination, a close general election is still likely.

Can the Democrats reunite after this?

Both candidates promised this weekend that they would work tirelessly for the other if they lose. But what began as collective excitement among Democratic voters at the beginning of the year has turned into mutual loathing for many.

The party has been cleaved along lines of race, gender, class and age. If Mr Obama has the nomination taken from him, African-Americans — the party’s most reliable voting bloc — will feel betrayed and will be likely to boycott the general election in large numbers.

Times Recommends

• No cause for celebration in crushed Sarajevo
• Jazz funeral for the final victims of Katrina
• French fined for 'insulting' civil servants