A Gallup Poll Daily tracking survey taken Wednesday through Friday of 1,231 U.S. adults indicates Obama, of Illinois, leads Clinton, of New York, among Democratic voters 52 percent to 44 percent.

This is Obama's eighth straight day of leading Clinton in the polls. He has led Clinton in every Gallup tracking report excluding a May 12 survey.

While Obama enjoys an increasing margin of support in the Democratic Party, he is statistically tied with presumptive Republican presidential nominee, Sen. John McCain of Arizona, in a survey of 4,460 national voters.

Clinton, however, beats McCain 49 percent to 45 percent, though the 2 percent margin of error in the national survey makes that lead statistically negligible.

The Democratic survey quoted a margin of error of 3 percentage points.