Barack Obama leads John McCain by three percentage points in the Newsweek poll released on today, a marked change from the Democrat's 15-point lead last month.
Democratic candidate Senator Obama captured 44% of respondents' support in the poll, compared to Republican opponent Senator McCain's 41%, a statistically-insignificant margin.
15% were undecided.
A 20 June Newsweek poll showed Senator Obama leading 51% to Senator McCain's 36%.
In the new poll, 53% of voters, including 50% of those who formerly supported Mr Obama's Democratic rival Hillary Clinton, believe that Mr Obama has changed his position on key issues in order to gain political advantage.
The poll surveyed 1,209 registered voters, and had a margin of error of plus or minus three percentage points.
