The demographics favor republicans as explained by John Fund on the Trail: "The best chances for Democrats to gain the 15 seats they need to take control of the House in 2006 are in these districts held by 'Kerry Republicans.' The problem is that there are so few of them. John Kerry carried just 18 GOP House members' districts, while Mr. Bush carried 41 Democratic ones."
"...Only five Republican House members currently sit in districts where Mr. Bush won less than 47% of the presidential vote last year: two in Connecticut, two in Iowa and one in Delaware. But 31 House Democrats represent districts where John Kerry won less than 47%. That means Republicans have many more opportunities to pick up seats in favorable political terrain as Democratic members leave the House. No one expects Democrats to hold the seat of Ike Skelton of Missouri when he leaves office; President Bush won 64% of his district's votes. Ditto for the district of Gene Taylor of Mississippi, where Mr. Bush won 68%."
"...Another worrisome sign for Democrats is the Hispanic vote. Michael Barone, a co-author of the definitive Almanac of American Politics, reports that Polidata's findings tend to confirm the exit polls that showed George W. Bush gaining nine percentage points among Hispanic voters, ending up with some 44%."