Now one would expect significantly better results for Republican candidates in a midterm, given turnout differences and second-term fatigue and all the rest. I expect better results. But still: This kind of pattern is consistent with a deeper reality, which is that the G.O.P. is still a weak party with a weak message, and weak parties with weak messages have a way of underperforming the fundamentals, struggling in races that feature larger electorates and more persuadable voters (hence the Senate-House difference), and losing narrowly where they confidently expect to win.
The Arkansas race is a case in point. By most accounts, the Republican challenger Tom Cotton is one of the best recruits for this election cycle that the party has, he is running against a somewhat unpopular incumbent in a state that overwhelmingly disapproves of Obama, and he still isn’t ahead of Pryor . I doubt that he trails him by a 10-point margin, but he shouldn’t be trailing at all. Among likely voters, the race is clearly close, but by all rights Cotton should have a sizable lead. The trouble for Republicans is that one of their top Senate candidates is in a dead heat or possibly losing in a state where he is considered the slight favorite. If that’s true for Cotton, it is difficult to see how the GOP will pick up enough seats to win a majority.
The numbers for Democratic incumbents can’t be encouraging for Republicans, but what ought to worry them a lot more is what the polls have been showing in Kentucky. In a year that ought to favor Republicans strongly, none of their incumbents should be vulnerable in the absence of some scandal, but McConnell’s challenger  is running even with him. McConnell will presumably hang on to win, but the fact that there is some question whether he will is a warning to the GOP that things are not going nearly as well for them this year as they expect. It may be that there are enough voters wary of giving Republicans control of both chambers that their individual Senate candidates are struggling to pick up otherwise winnable seats.