PRINCETON, NJ -- As the national political conventions are poised to start, the party orientation of U.S. voters clearly favors the Democratic Party, similar to the pattern seen for the past five months. Among all national registered voters interviewed thus far in August for the Gallup Poll Daily tracking survey, 35% identify as Democrats compared with 28% who identify as Republicans. An additional 36% are independents.
The current 7-point Democratic advantage in party ID expands to 10 points when the party leanings of independents are taken into account. Fifty percent of U.S. registered voters identify with or lean to the Democratic Party and 40% are Republican or lean Republican.
This Democratic advantage contrasts with the close nature of the presidential contest between Democrat Barack Obama and Republican John McCain in monthly averages of the Obama vs. McCain horse race since March.
Although Obama has led by as many as 9 percentage points over McCain in Gallup Poll Daily tracking three-day rolling averages, the results on a monthly basis show Obama averaging no better than a 3-point lead among registered voters in any month. This includes August (according to interviews from Aug. 1-19), during which Obama has led 46% to 43% (though in the past week, Obama has averaged just a 1-point advantage).
Gallup's most recent weekly aggregate, based on Aug. 11-17 data, found Obama up by an average of only 2 points over McCain, 45% to 43%. At the same time, voters' party preferences broke 35% Democratic and 28% Republican (with a 50% to 40% Democratic advantage on party identification, including leaners).
The reasons this is not translating into a stronger lead for Obama are twofold:
1. Although Democrats outnumber Republicans in the electorate, McCain receives the support of a greater share of his party base than does Obama.
Whereas 84% of Republicans polled from Aug. 11-17 say they will vote for McCain in November, only 79% of Democrats say they will vote for Obama. A similar gap in party loyalty has been seen each week since Obama clinched the Democratic nomination in early June. Over this period, Obama's Democratic support has ranged from 78% to 82% while McCain's Republican support has ranged from 83% to 85%.
2. The race has been extremely close among the roughly 36% of voters who call themselves political independents.
Since early June, Obama and McCain have swapped the lead among independents, with neither ever achieving a very large lead. Overall, Obama has averaged just a 1-point lead over McCain among independents, and in interviews conducted Aug. 11-17, the two were tied at 42%.
Given the stability in support for Obama and McCain among their respective party regulars, and the underlying stability in the party identification of voters, nearly all of the movement in the overall horse race since early June -- ranging from a tie to a 9-point lead for Obama -- can be explained by shifts in support for the candidates among political independents.
More voters this year have aligned themselves with the Democratic Party than the Republican Party. The Democrats have a 7-point advantage in terms of core partisans, and a 10-point advantage when factoring in the leanings of political independents.
If each candidate were supported equally by his partisans, and independents split equally, that would translate into a 7- to 10-point lead for Obama over McCain in the race for president. But the race has been closer than that, primarily because a greater proportion of Republicans than Democrats are backing their own party's candidate for president.
Going into the convention period, it thus appears that a crucial test for Obama will be winning over heretofore reluctant Democrats to his candidacy, and the challenge for McCain will be retaining his Republican base. The vice presidential selections could be key factors in both cases. At the same time, both candidates will face the challenge of attracting more independents to their candidacies. In a close race, even a slight swing in the preferences of this group could be decisive.
For the Gallup Poll Daily tracking survey, Gallup interviews no fewer than 1,000 U.S. adults nationwide each day, generally including approximately 880 registered voters.
The average weekly results reported here are based on combined data from approximately 6,200 registered voters interviewed each week from Monday through Sunday. For results based on samples of this size, the maximum margin of sampling error is ±1 percentage point. For results based on subgroups of registered voters, the margins of sampling error are higher.
The average monthly results reported here are based on combined data from at least 21,000 registered voters for each month from March through July, and 13,198 registered voters for the partial month of August (Aug. 1-19). For results based on samples of this size, the maximum margin of sampling error is ±1 percentage point. For results based on subgroups of registered voters, the margins of sampling error are higher.
Interviews are conducted with respondents on land-line telephones (for respondents with a land-line telephone) and cellular phones (for respondents who are cell-phone only).
In addition to sampling error, question wording and practical difficulties in conducting surveys can introduce error or bias into the findings of public opinion polls.
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