The NRA was absent for the midterms.
NRA spending was much reduced for the 2018 midterms, but it was there. The principal reason? It busted the budget in 2016 rooting for the GOP, spending almost 3x as much is in 2012.
https://www.opensecrets.org/orgs/summary.php?id=d000000082&cycle=2018
Part of the problem is probably complacency on the part of gun owners (aka NRA members and donors), now that a GOP president is in office.