But while Mr Kerry has extended his lead nationally, a regional poll conducted simultaneously shows that the electoral battleground remains evenly divided in the key swing states, which he must win if he is to become president in November.
In a two-way contest, Mr Kerry leads Mr Bush by 51% to 44%. In a three-way race that includes the independent, Ralph Nader, Mr Kerry leads 48% to 42%, with Mr Nader on 4%. Mr Kerry's prospects have been boosted by the fact that a growing proportion of Americans - about 60% - believe the country is on the wrong track. It is the highest figure recorded by an LA Times poll during the Bush presidency.
The improving economy and United Nations endorsement of the June 30 handover in Iraq appear to have done little to bolster Mr Bush, with 56% of Americans saying the US "needs to move in a new direction" because his policies have not improved the country.
But while the general message is encouraging for Mr Kerry, the news from some marginal states is more bleak. Detailed polling in Missouri, Wisconsin and Ohio shows Mr Bush either ahead or neck and neck with the Massachusetts senator.
During the 2000 election, the Republicans won Missouri and Ohio and lost Wisconsin in tight races. The poll suggests a possible rerun of that election, where the Democrats won more votes nationwide, yet lost the election because they did not win enough states.
It also suggests that in those areas where both campaigns have flooded the airwaves with attack ads, Bush is faring better than his challenger. Data compiled by the LA Times shows that the Republicans have spent more than $15m (£8.17m) in the three marginal states, while groups supporting Mr Kerry have spent $25.6m.
When those with negative opinions about Mr Kerry were asked to explain them, the most common response was to parrot the key claim of the Bush ads - that he "flip-flops" on issues for political advantage.
While Mr Kerry was a big hit with Democrats during the primaries, the poll suggests he has failed to capture the imagination of many voters, which has allowed Mr Bush to set the agenda with regard to his character.
More than one third of voters nationally, and nearly half of independent voters, said they did not know enough about the Massachusetts senator "to decide whether he would be a better president" than Mr Bush.
While some critics within the Democratic party accuse Mr Kerry's campaign of being too slow off the mark, Mr Kerry's advisers say they are playing a long game and that Mr Bush has already lost the advantage of incumbency.
More than half of all voters say they disapprove of the president's handling of the economy and Iraq, while his approval ratings are only marginally positive, at 51%.
Every sitting president with approval ratings below 50% at this stage has lost. Those who have won have generally had approval ratings above 55%.
The only area of policy in which Mr Bush performs well is his handling of the war on terror, although Mr Kerry is closing the gap.
With Mr Bush having made a great deal of his resolve to act on gut instincts, however, a huge majority, 58% to 16%, believe the phrase "too ideological and stubborn" applies more readily to him than to Mr Kerry.
But while the public have cooled towards Mr Bush, they have yet to warm to Mr Kerry's values and personality - crucial factors in an election. Asked which man shared their moral values, 45% said Mr Bush and 36% Mr Kerry. A recent Quinnipiac poll revealed that while most would rather have Mr Kerry teach their children, they would prefer Mr Bush at their barbecue.
Overall the nation still remains evenly divided and keenly polarised. More than 80% of those who approved of the president's performance said they would vote for him, while more than 90% of those who disapproved said they would not.
