US election: Guide to the battle

The candidates face the task of winning over key groups of waverers without alienating their core supporters.

Young people have consistently been Barack Obama's most enthusiastic supporters. A Pew Research Center poll published on 21 October indicates he's supported by 66% of people under 30, compared to 27% for John McCain. Getting these young people to turn out to vote is a key challenge for the Democrats.

Mr Obama also enjoys an 20% advantage among women. Single or divorced women are most likely to back the Democratic candidate, married women are more evenly divided.

For much of the campaign, Mr McCain was ahead among men, and voters over 65. However, a number of polls indicate that his lead in these groups has evaporated. The latest Pew poll has the candidates tied on 44% among voters over 65, and gives Mr Obama 5% advantage among men.

The battle for the working-class male

Mr Obama has made even more striking gains among non-Hispanic Catholics. In September, Pew registered a 7% lead for Mr McCain in this group, in mid-October Mr Obama led by 48% to 41%.

An earlier poll found that Mr Obama had a nearly two-to-one lead among Hispanics, which could prove key in several battleground states, such as Colorado, Nevada, New Mexico and Florida.

Afro-American voters are strongly Democratic, which could help Mr Obama in Virginia and North Carolina.

The nomination of Sarah Palin as the Republican vice-presidential candidate helped mobilise evangelical Christians for Mr McCain. He leads Mr Obama by 67% to 24% in this group. A major task for the Republicans is to ensure they turn out to vote.