Washington (CNN) The Democratic advantage on the generic congressional ballot has tightened to 6 percentage points, a new CNN poll conducted by SSRS finds.

The poll finds that 50% of registered voters say they prefer a Democrat in their congressional district, while 44% say they want a Republican. That's a major shift in favor of the GOP since February, when Democrats held a 16-point edge. It's much closer to January, when their lead was just 5 points.

But Democratic voters are much more enthusiastic about casting ballots in November's midterm elections.

About half -- 51% -- of Democrats and Democratic-leaning independents say they are extremely or very enthusiastic about voting for Congress in November, compared with just 36% among Republicans and Republican-leaning independents.

And at the same time, those voters who are deeply enthusiastic about voting give Democrats a better than 20-point lead on the generic ballot: 60% prefer the Democrat in their district, while 38% who prefer the Republican.

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