Trump won suburbs of major liberal us cities in 2016 and didn't in 2018. It wasn't because conservatives didn't vote. Trump won in some places that Romney didn't, McCain didn't.
Lost 9 seats in NY, NJ, PA, NoVA - the I 95 corridor, pretty much.
Upper middle class folks gave Trump a shot, and got tired of being called a nazi by upcs. So, maybe some of those stayed home, and some of the women mad about Kavanaugh, or whatever faction of the dem coalition lives in the suburbs, probably them. Every year some people change their minds other people stay home other people are motivated to vote.
Wasn't a problem with Conservatives this year. North Dakota went GOP this year, so did Indiana and Missouri. Conservatives didn't show up in those states in 2012, when Romney was unappealing to Conservatives