The Cook Political Report is back with new ratings of House seats, and by general agreement the "takeaway" is that Democrats have more to worry about than Republicans. Eight of the nine pure "toss-up" races are in districts now held by Democrats; Sixteen of the 27 races "leaning" one way are leaning just a little toward Team Blue.
What this actually tells us is that gerrymandering works wonders. Seven of the nine toss-ups are in California, Florida, and Arizona. What do those states have in common? California drew its new lines after voters passed a referendrum that turned maps over to a non-partisan commission. Arizona's map was drawn by an independent committee, even after Republicans tried to purge said committee. Florida passed a "fair districts" law in 2010, and Republicans basically tried to ignore it, but they ended up drawing a couple more Democratic seats anyway and litigation is ongoing.
There are some gerrymandered districts on the list, sure -- Illinois's Democrats ended up with a few seats that merely lean their way -- but look at what's missing from the map. North Carolina, which has 13 districts and has split nearly 50-50 at the presidential level, has only one competitive race (in a seat drawn to elect a Republican but held narrowly by a Democrat). Pennsylvania, which has voted Democratic for president since 1992, has a 13-5 Republican majority in its delegation. Only two seats are even on the map, and they're still "likely" Republican -- a Democratic landslide would probably end with Republicans holding a 11-7 majority. But California has a total of nine competitive seats. New York, whose map was designed in a compromise between the Democratic Assembly and Republican Senate, has seven competitive seats.