PRINCETON, NJ -- Gallup's final pre-election allocated estimate of the national 2008 vote for Congress -- from Gallup Poll Daily tracking conducted Oct. 31-Nov. 2 -- gives the Democrats a 12 percentage-point lead over the Republicans among likely voters, 53% to 41%. The Democrats have led on this measure in Gallup polling for most of the year, except for one survey after the Republican National Convention in September.
The final estimate is based on Gallup's traditional likely voter model, and assumes a turnout rate of 64% of the voting-age population. However, the Democrats' advantage among traditional likely voters is not much different from their standing among all registered voters, among whom they hold a 15-point lead.
The generic ballot indicates what percentage of all votes cast nationally for Congress (when the votes cast in each of the 435 individual U.S. House of Representatives districts are aggregated) will go to each party's candidates collectively. Historically, this measure has been a highly accurate predictor of the national two-party vote for Congress in midterm election years and, as a result, can be used to accurately forecast the number of seats each party will win in midterm years. In presidential election years, however, it is a somewhat less reliable indicator of the national two-party vote and, therefore, of seat change.
Still, in broad terms, the Democrats' current advantage on this measure points to significant gains for the Democratic Party in Congress. In 2006, Gallup found the Democrats with an 11-point lead among registered voters, and a 7-point lead among likely voters, right before the election. The Democrats won 54.1% of all votes cast nationally for Congress, and a 31-seat advantage. On that basis alone, their current 12-point generic ballot lead could result in a higher share of the two-party vote than they had in 2006.
There have been only two presidential elections in the last 40 years in which the Democrats have held a double-digit lead on the generic ballot going into Election Day in a year when the Democratic candidate for president won. But in neither case did the Democratic ticket win the election by a large margin, such as Barack Obama and Joe Biden seem poised to achieve on Tuesday.
The most recent case was 1992, with Bill Clinton running as the Democratic nominee for president. However, the Democrats' congressional gains may have been blunted in that election by the fact that the strong support for third-party candidate Ross Perot suppressed popular support for Clinton. Clinton won the presidential election in 1992 with 43% of the popular vote, and the Democrats won just 52.8% of the two-party vote for Congress.
In the second instance, in 1976, the Democrats held a 14-point lead on the generic ballot among likely voters immediately before the election. They won 54.5% of the two-party vote for Congress, but that was with their Democratic presidential nominee, Jimmy Carter, barely beating Gerald Ford, 50% to 48%. The Democrats might have won an even larger share of the vote had Carter run more strongly at the top of the ticket.
In 1980, the Democrats held a 15-point lead among registered voters on the generic ballot, but with Republican presidential candidate Ronald Reagan winning that election by a 10-point margin over Jimmy Carter, the Democrats' congressional vote was held to only 51.3%.
The Democratic Party enters Tuesday's election with a 36-seat advantage over the Republicans in Congress, 235 vs. 199 (with one vacancy). Given their 12-point advantage among likely voters on the generic ballot, and the fact that their presidential candidate appears poised to win the election by a large margin, it appears that the Democrats could be on the verge of a major gain in U.S. House seats.
Vote for Congress Highly Partisan
A high degree of Republicans and Democrats are supporting their own party's congressional candidate in this election: 94% among Democrats and 91% among Republicans. Political independents are tilting toward the Democrats, with 46% voting Democratic and only 40% voting Republican.
It also appears that not much ticket splitting is going to occur: 91% of voters who back the Obama/Biden ticket for president plan to support the Democratic candidate for Congress in their district; 87% of voters backing John McCain and Sarah Palin plan to vote for the Republican candidate.
Results are based on telephone interviews with 3,050 national adults, aged 18 and older, conducted Oct. 31-Nov. 2, 2008 as part of Gallup Poll Daily tracking. For results based on the total sample of national adults, one can say with 95% confidence that the maximum margin of sampling error is ±2 percentage points.
For results based on the sample of 2,824 registered voters, the maximum margin of sampling error is ±2 percentage points.
Results for likely voters (based on Gallup's "traditional" likely voter model or likely voter model I) are based on the subsample of 2,472 survey respondents deemed most likely to vote in the November 2008 general election, according to a series of questions measuring current voting intentions and past voting behavior. For results based on the total sample of likely voters, one can say with 95% confidence that the margin of sampling error is ±2 percentage points. The likely voter model assumes a turnout of 64% of national adults. The likely voter sample is weighted to match this assumption, so the weighted sample size is 1,952.
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.