On the latter point, I've found the defenses I've read so far of Booker's vote relatively limp. That said, I think the best take has come from (of all people) Erik Loomis:
Cory Booker has a reasonably high chance of being the Democratic nominee in 2020. There are good reasons for this. He gave a great speech at the DNC that really rallied everyone who heard it against hate. Given the amount of hate that is coming, this is a good thing. His testifying against Jeff Sessions was excellent. He is charismatic and has a great chance of reviving the Obama coalition. That charisma and leadership potential is absolutely crucial for whoever the nominee is going to be.
At the same time, the nominee is almost certainly to be someone who can speak to some sort of economic populism. Maybe that can be Cory Booker. But he has a lot to answer for. His embrace of charter schools and the inherent anti-unionism involved in them made him a heck of a lot of enemies. So have his close ties to Wall Street. And now we have him voting against allowing the importation of prescription drugs from overseas. All of these are real problems for him and should make us ask him very hard questions. I get that he is from New Jersey. He is also basically untouchable in that state. He can defy Wall Street and the Big Pharma companies based in New Jersey to run for the presidency. He needs to if he indeed is going to do that. Unfortunately, he does not seem to understand that. And thus he is going to be rightfully criticized from the left.So it strikes me as entirely right that liberals should be putting pressure on Booker to adopt better positions on economic matters. Maybe they'll be successful, maybe they won't. Most likely, we'll see some tack to the left but less than many in the base would have liked -- which is the nature of the beast.
What I will predict is that, even if Booker does perform admirably between now and 2020, there is a cadre of "progressives" for whom it will never be enough -- his past positions make him an inherent nonstarter. They will say that Booker is only pandering, that he isn't a true believer -- not understanding that the point of political action is to get politicians to decide that your position is one worth pandering to. The difference between liberal and conservative politicians isn't that the former come preloaded with the dream progressive agenda. The difference is that liberal politicians are susceptible to liberal political pressure in a way conservatives aren't. Whatever else he is, Cory Booker is a liberal in this respect -- he can be influenced from the left.