A profile of the Democratic front-runners
Barack Obama
Obama is focusing on states that hold caucuses, where his powerful grassroots organisation has a clear advantage in persuading committed supporters to show public support.
He is targeting states such as Alaska and Idaho, which are often ignored by Democrats, but he is also confident of winning in Georgia and Alabama, which have large African- American populations. Obama should win his delegate-rich home state of Illinois but he will also win delegates in states such as California and New York, and he is advertising in 20 out of 22 states that vote on Tuesday.
Obama's support base includes students, the better-educated and the well-paid, but he also has the support of the majority of black voters and expects to win many independent voters in states where they can vote in the Democratic primary.
Hillary Clinton
Still ahead in national polls, although her lead is narrowing, Clinton expects to win more votes than Obama in the most populous states on Tuesday and to rack up big delegate numbers in her home state of New York, neighbouring New Jersey and California, where she has spent the last three days. The former first lady should also win in Arkansas and Oklahoma and she is hoping to win Massachusetts, despite Obama's recent endorsement by the Kennedy clan.
Clinton's strength is among women, older voters, blue-collar workers, voters without a college education, and Latinos, but she is campaigning hard to retain the support of a sizeable minority of African-Americans. She retains the loyalty of the party leadership in many states, a factor that could prove crucial in getting out the vote on Tuesday.