Arnold Kling notes that exit polls show that 52% of those who voted have an unfavorable opinion of the Democratic Party and 53% have an unfavorable opinion of the Republican Party. Arnold comes up with this conclusion:
People with an unfavorable view of Democrats went 88-10 for Republicans, but people with an unfavorable view of Republicans only went 76-22 Democrat.
That was the difference in the election. The “unfavorables” on net broke Republican. The way I would spin it is that there is a large block of voters who are negative on both parties, the Republicans captured a larger share of that block, and that block swung the election.