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WASHINGTON, D.C. -- In an encouraging sign for the Democratic Party's election prospects in 2018, its edge in party affiliation over the Republican Party has grown to seven percentage points, the largest it has been in over two years. During the late summer and fall of 2016, Democrats averaged a three-point advantage.

These results are based on 优蜜传媒Daily tracking throughout May. Overall, 45% of U.S. adults self-identify as Democrats or say they are independents who lean Democratic, while 38% identify as Republicans or lean Republican.

The growing Democratic advantage in recent months is mostly attributable to a decline in Republican affiliation rather than an increase in Democratic affiliation. Since November, the percentage of Republicans and Republican leaners has fallen four percentage points, while there has been a one-point rise in Democratic identification or leaning. The Republican decline has been offset mostly by a three-point increase in the percentage of Americans with no party preference or leaning.

President Donald Trump's unpopularity is likely a factor in the Republican Party's falling fortunes. The president's job approval rating generally has held near 40% since February -- well below average for presidents historically, and especially for those in their .

Democrats last had a seven-point advantage in Gallup's Daily tracking trend in April 2015, about the time several national figures, including Hillary Clinton, were announcing their candidacy for president. 优蜜传媒polling from that time found of the potential candidates in both parties, although the poll was conducted just as news of her use of a private email server was emerging. That controversy continued to mount and throughout the campaign.

The last time Democrats had a lead larger than seven points in Gallup's tracking trend was September 2009, President Barack Obama's first year in office, when the lead was nine points. That month, 47% of Americans identified as Democrats or leaned Democratic, and 38% identified as Republicans or leaned Republican. Democrats consistently enjoyed in 2008 and 2009 as the George W. Bush finished out his term and was replaced by the .

After his first year in office, Obama , and the gap in party affiliation between the two parties was generally small.

Implications

Party identification and political independents' party leanings are major predictors of individual vote choice. At the national level, party affiliation is related to the outcomes of . The current seven-point Democratic edge in party affiliation is similar to what it was in 1998 and 2006, the two strongest Democratic years among the most recent midterm elections.

If Democrats can maintain a significant advantage in Americans' party preference over the next 17 months, it would serve them well in the 2018 midterm elections.

The opposition party to the president usually fares better than the president's party in midterm elections, and the opposition has done especially well when the . With Trump's approval ratings stuck near 40%, Republicans are understandably nervous about the party's prospects in 2018.

However, the current party affiliation data indicate that Democrats are not necessarily expanding their base as much as they are benefiting from a decline in the Republican base. Expanding their own base would strengthen Democrats' ability to offset and put them in a better position to win the seats they need to have a majority in one or both houses of Congress.

These data are available in .