As the election race for the Democratic nomination tightens ahead of Super Tuesday, both Hillary Clinton and Barack Obama are frantically criss-crossing the country, while trying to mobilise their key supporters across the board.
Several national opinion polls released over the weekend show that Hillary Clinton's lead in the polls has narrowed dramatically.
According to a new Washington Post/ABC News poll, Mrs Clinton's lead among likely Democratic voters has shrunk to 47% against 43% for Mr Obama, while the latest CBS News poll finds Mr Obama in a tie with Mrs Clinton with 41% each.
In early January Mrs Clinton was ahead of Mr Obama by up to 15% in national opinion polls.
Both new polls were conducted last week on 30 January - 1 February, and have a sample size of 1,232 and 1,241 respectively.
The close contest makes it vital for both candidates to reach their key supporters.
Ms Clinton is emphasising her experience of office
Mrs Clinton spent much of last week in California, the biggest prize among primary states last week, before crossing the continent over the weekend.
She is hoping that the strength of women among California Democrats - including two Democratic Senators and the speaker of the House of Representatives - will help boost her chances.
She also stopped in Arizona and New Mexico, trying to rally Hispanic voters who are among her strongest supporters, before taking her campaign to Mr Obama's home state of Illinois (where Mrs Clinton was born).
She is finishing her dash in her northeast stronghold, visiting Massachusetts, Connecticut and her home state of New York.
For Mrs Clinton, it is vital that she retains the support of three key groups - women, older Americans, and working class voters, especially those worried about the economy.
Mrs Clinton is seen as the most experienced of the Democratic candidates, and is rated highly on her ability to deal with key issues, especially on the economy, the top issue for most voters.
So Mrs Clinton's television advertising has focused on this issue, with her economic plan providing a parachute for voters who are falling into economic difficulties.
Mr Obama is drawing enthusiastic crowds
Mr Obama, boosted by his fundraising success in January, is now challenging Mrs Clinton across the country, after consolidating his base among black voters in the South.
He is now leading more than two-to-one among black voters, and even older black women seem to have come over to his camp.
Mr Obama has had less success among Hispanics in recent primary elections, but he is now running commercials in Spanish and deliberately visited both southern California and New Mexico last week as he frantically crossed the country three times.
He is running particularly strongly among men, where he is now even with Mrs Clinton, and among independents and voters who consider themselves "liberal."
Race, age and gender are all key factors at play
So Mr Obama has decided to take his campaign into Mrs Clinton's backyard, holding rallies in the last few days in New Jersey and Massachusetts as well as trying to shore up his black voters in Delaware.
Mr Obama is also running strongly among young voters, and among those higher education, and especially post-graduate education.
He is hoping that the enthusiasm of his young supporters will help get out his vote in the key battles on Tuesday.
And Mr Obama is clearly the candidate of those who believe "change" rather than experience is the most important quality of the person they vote for.
But Mr Obama still has some major challenges.
Among voters in the states which are actually voting on Tuesday, he is trailing Mrs Clinton by 49% to 31%, according to the CBS News poll.
And Mrs Clinton's supporters back her more strongly, with 60% saying they strongly support her strongly, compared to 50% for Mr Obama.
But with 14% of Democratic voters saying they still haven't made up their mind, there is still everything to play for.
1 San Jose/San Francisco, California
2 Los Angeles, California
3 Phoenix, Arizona
4Albuquerque, New Mexico
5 Minneapolis/St Paul, Minnesota
6 Chicago, Illinois
7 Boston, Massachusetts
8 Hartford, Connecticut
9 New York City, New York
1 Albuquerque, New Mexico
2 Boise, Idaho
3 Minneapolis/St Paul, Minnesota
4 Chicago, Illinois
5 St Louis, Missouri
6 Los Angeles, California
7 Wilmington, Delaware
8 Chicago, Illinois
9 Salt Lake City, Utah
10 Bergen Co, New Jersey
11 Boston, Massachusetts
Source: Press reports (1-4 Feb only)