The N.R.A. still has considerable clout with Republicans, including President Trump and Senate leaders, and it is now flexing its muscles in the debate over background checks. Yet for many years, the group’s influence was broader and deeper because of its large numbers of friends in both parties. These political allies received “A” ratings from the N.R.A. and often feared grade reductions if they crossed it.

Now, the number of Democrats in the House with “A” ratings has fallen from 63 after the 2008 elections to three after the 2018 midterms.

This makes the N.R.A.’s political position more precarious. The group was once largely insulated from shifts in partisan control: It could block gun restrictions no matter which party controlled Congress and the White House. In the long term, the loss of the N.R.A.’s Democratic buffer poses a threat to the group’s influence no matter what happens in the current gun control debate.