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A new Fox News poll asked likely voters to choose between the Democratic and Republican candidates in their congressional districts.

Democrats were up six points, 48-42 percent, compared to 44-43 percent at the end of September.

Karl Rove joined Brit Hume on "On The Record" and said that if that gap grows to eight or nine points, it could signify a "wave election" and real trouble for the GOP.

He explained that these numbers are roughly where they were in 2008, when Republicans lost 20 seats in the House.

"They'd need to lose 30 to lose control of the House, but this number had better not be getting worse, and they've got to find ways to get it better."

Hume noted that Democrats have a long shot at taking the House, but they have high hopes for taking the Senate.

He asked which races will particularly critical for Republicans if they want to maintain control of the Senate.

"If you had to pick only a couple, I'd pick Nevada, Indiana, Missouri, North Carolina," Rove said. "[If] Republicans can take three or four of those, they've got a good shot at being in the majority."

Get more insight from Rove above.

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