Probably gonna regret this, but since I'm going to work in less than 2 hours..
Sanders's reasoning for his vote is 'I don't trust the guy'. Hardly nuanced reasoning, more of a gut feeling about W. He's probably a good judge of character, or maybe his isolation from his peers and fringe political beliefs make him much more suspicious of establishment politics, or maybe another reason. Still, I find it strange to say the least that the Iraq war vote is repeatedly leveled at Clinton despite her numerous apologies and explanations, while John Kerry, Joe Biden, John Edwards got nowhere near the same scrutiny, having vote for it themselves. Dianne Feinstein voted for it. Is she a neocon? That's a disastrous invasion that did much harm to the region and the world, but you know what equally destructive invasion that Sanders voted for? Afghanistan. The question about Iraq is the legality of the invasion, and on that ground it's much worse than Afghan, but both have been equally corrosive for the region's stability and US foreign policies going back decades are the roots of the problem. None of this absolve her from part of the blame, but it's important to note that the chief culprits are the Bush administration.
What I meant by tanks is merely to draw an analogy. If the auto industry are allowed to release millitary grade vehicles to the general populace, and dipshits start buying them en masse, creating pollution, infrastructural damage and accidents, wouldn't you think it'd be fair to hold them accountable? Not to mention that firearms in and of itself is a different question altogether. Their chief purpose is to kill and I think it's reasonable to hold the manufacturers recklessly flooding the market with those death tools without regards to the wellbeing of people accountable. Sanders himself has wavered on this issue btw, and while he still doesn't officially espouse the position yet, why isn't it a legitimate question that families of the victims should be able to seek redress? I fecking hate guns so yes, it might cloud my judgement, but if my mother was shot dead by death tools that have no business being in public, I'd make sure that producers of those weapons get hell for it, and the one I vote for support my effort. Why shouldn't the industry be held liable for damages so that they are more responsible with their products? It actually seems far more likely that such laws will have a more positive effect than the numerous checks and assault weapon ban being touted.
On the final point, I'm not naive enough to believe that, but moneyed interests negotiate with politicians, some more than the others. Bernie Sanders got large donations from the farming industry, which is responsible for about 15% of greenhouse gases, and he voted in their favor consistently. Is he corrupt? No, but politicians usually have one or two core positions they will not compromise on, and the rest is negotiable to various degrees. Obama's is healthcare and gun control, Hillary's is gender equality and advocacy for children (healthcare, childhood education) and Bernie's is income inequality. Politicians say a whole lot of guffs. Id rather look at their legislative record to know their true positions, rather than what they say to the electorate.