Not quite, but let’s call it close enough, because I think it misses the real point.
Political power is about more than just the instrumental analysis of counting up the number of Democrats and concluding they can do anything they damn well please. Actual politics is way more complicated than that. It involves primary threats, public perception, outside attacks, political capital, and a dozen other factors. Political actors are constrained by more than their consciences, and so if we’re going to analyze the failure to exercise political power, we have to do more than just count numbers.
I think there can be little serious doubt that the reason the Democrats didn’t do more to fund ATF is because of the Republicans and the NRA, and to a lesser extent because some of those Democrats agree with the Republicans and the NRA.
Why do we care to assign such abstract blame? Because the solution involves pushing back against whatever levers of power are causing the result we don’t like. Those who think the ATF should enforce the laws on the books need to first identify the cause of the failure to do so before planning a solution.
We’re seeing that now, aren’t we? He finally wants to try to appoint an actual head of the ATF, for example. As to “why not earlier,” I think there are a half-dozen plausible reasons: he didn’t think he had the capital, he didn’t understand the issue, he knew Congress wouldn’t go for it, he was focusing on other more important things, etc. etc.