In a 2016 exit poll I saw that 13 percent of house GOP voters said they voted for Hillary Clinton. Only 10 percent of house Democratic voters said they did the opposite.
Was this also true under Obama? Don’t go back any further than 2008 or maybe 2004 because that is when/after most voters slowly stopped splitting tickets. In other words: are Republican voters more likely to vote Democrat than Democratic voters are to vote Republican?
Here is the CNN poll: https://edition.cnn.com/election/2016/results/exit-polls