The NRA has significant financial advantages in having “non partisan” not for profit status.
It doesn’t mean that they have to endorse Democrats. But does mean that their endorsement criteria must be applied evenhandedly and transparently, without consideration of Party.
If a Democrat meets their endorsement criteria, that Democrat will get their endorsement. Regardless of the bigger partisan picture and if only to prevent giving the IRS cause to launch an investigation into their not for profit status
Which explains Manchin.
Perhaps less time spent trying to balance on the head of a pin and more time preventing anyone from engaging in activities contrary to “shall NOT be infringed” would be more productive. The lines are drawn, the enemy is known, playing both sides cannot work anymore if it ever did seeing just three major gun giveaways of the Congress in 1934 NFA, 1968 and 1986. Without those acts things might be somewhat reasonable in my mind anyway.