Even worse, The 1968 GCA was DOA until the NRA got involved and got Charlton Heston and company to back it.
I believe you have been mislead about what happened.
The NRA did not "proudly" back the NFA of 1934, GCA of 1968, or the 1986 machine gun ban.
The NRA in 1934 was not consulted about the NFA of 1934, which the president of the NRA complained about in the committee hearing. It was in large part because of the NRA that pistols and revolvers were stripped from the bill, mostly neutering it. Silencers were included, mostly by mistake, and short barreled rifles were added by the Congressman from Minnesota.
Then the NRA backed what was left as part of the compromise. Very few people had silencers or machine guns.
It was very similar with GCA 1968. The NRA opposed it. I recall the notices sent out as my father belonged to the NRA at the time. President Johnson was the big one pushing it, and he managed to get it through by a one vote majority. The NRA lead the opposition, but yes, they also worked at mitigating how bad the bill was. Originally, it included total registration and licensing of pistols. President Johnson bitterly complained that those items had been stripped from the bill.
As for the (Huges Amendment) Machine gun ban of 1986, that was passed as part of the Firearm Owners Protection act of 1986, forced out of committee by a dogged fight led by the NRA, which took years. The amendment freezing the number of machineguns in civilian hands was sprung on the Congress with a voice vote under dubious circumstances, but which was legal. The video is online. The NRA did not push for that.
However, to get the real reforms of the GCA 1968 which were in the Gun Owners Protection Act of 1986 (transport of firearms across state lines, no record keeping of ammunition, ammo allowed to be sold by mail, as I recall, gun dealers allowed to sell at gun shows) reform of some of the worst of GCA 1968) they had to accept the amendment.
So, are the NRA's fingerprints on NFA 1934, GCA 1968, and the FOPA Huges amendment in 1986? Yes, but they also prevented a whole lot of worse things from passing.
Could the NRA have done better?
Maybe, probably, we don't know. Hindsight is 100%.
I stopped donating to the NRA about 1990. I figured my money was better spent on other groups, such as the Second Amendment Foundation, local groups in Arizona, such as Brass Roots, and others.
It is not fair to claim the NRA was responsible for NFA 1934, GCA 1968, and the Hughes Amendment to FOPA in 1986, unless it is mentioned what the original scope of the bills were, and what the NRA stopped from passing.