(CNN) More independents are saying they'll support the Republican candidate in 2018, which could be a warning sign for Democrats who hope an anti-Trump wave will help them seize control of the House majority.

The generic ballot -- voters are asked which party they'll support as opposed to a specific candidate -- has tightened in the most recent CNN poll , which was released in early May.

Forty-three percent of independents in CNN's most recent poll said they would vote for the Democratic candidate and 40% said they would support the Republican candidate, a small enough difference in the numbers that make them basically statistically equal.

While a generic Democratic candidate has been doing better than the Republican during all points of the 2018 cycle, at the beginning of the year, 50% of independents said they would vote for the Democratic candidate and 35% the Republican -- a 15-point gap in CNN's February poll that has decreased to 3 points in May.

The number of independent respondents saying "other" or "neither" to these options has increased to 11% in May from 4% in March. Independents are the most likely partisan group to say "other/neither" or "no opinion" -- at 11% and 6% respectively. Only 2% of Republicans have no opinion and 4% of Democrats. It's possible that independents are moving from "other/neither" or "no opinion" to make their decision, but it's still unknown at this point.

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