I am wondering whether Democrats are more firm in their voting patterns. What I mean by this is actually going out to vote. I mean only voting for the party they're registered with. (This doesn't necessarily include leaning independents but it might carry over.) According to the Kaiser Family Foundation, "A vast majority of Democratic voters (85%) and most Republican voters (70%) say they aren’t going to cast a vote for the other party’s candidate." That is a sizeable difference.
For example, I have read a study about swing voters in New Mexico in 2008 by AARP. It has found that 16% of swing voters were liberal. But, Pew's political landscape study found that around that time, 23% of adults in the state were liberal.
AARP: https://assets.aarp.org/rgcenter/general/swing_voters_nm.pdf Pew: https://www.pewforum.org/religious-landscape-study/state/new-mexico/political-ideology/ Kaiser: https://www.kff.org/other/issue-brief/data-note-swing-voters/
Final note: I mean firmness as in "loyalty". Loyalty means voting for candidates of that party no matter what.