It's dead even in a new national poll in the race for the White House.

And the survey also indicates that there's a major difference in motivation between supporters of President Barack Obama and Republican challenger Mitt Romney.

According to an ABC News/Washington Post poll released Tuesday morning, 47 percent of registered voters nationwide say if the November election were held today, they would vote for the president, with an equal amount saying they would cast a ballot for Romney, the presumptive GOP nominee.

The ABC News/Washington Post survey is the latest in a string of national polls released over the past two weeks to indicate the battle for the presidency either tied up or with only a slight edge for Obama.

While the horserace is all knotted up, there's a wide gap when it comes to motivation. Three-quarters of Obama supporters say their vote is for him, with just 23 percent saying they're voting against Romney. Only 37 percent of Romney supporters say their vote is for their candidate, with nearly six in 10 saying their vote is against Obama. There was a similar trend in President George W. Bush's 2004 re-election victory over Sen. John Kerry of Massachusetts, the Democratic nominee.

The ABC News/Washington Post poll was conducted July 5-8, with 1,003 adults nationwide, including 855 registered voters, questioned by telephone. The survey's sampling error for registered voters is plus or minus 4 percentage points.