Jezebel has a response from Booker on why he voted against the drug amendment:

I support the importation of prescription drugs as a key part of a strategy to help control the skyrocketing cost of medications. Any plan to allow the importation of prescription medications should also include consumer protections that ensure foreign drugs meet American safety standards. I opposed an amendment put forward last night that didn't meet this test. The rising cost of medications is a life-and-death issue for millions of Americans, which is why I also voted for amendments last night that bring drug prices down and protect Medicare's prescription drug benefit. I‎'m committed to finding solutions that allow for prescription drug importation with adequate safety standards.

Suuuuure. I'd be really concerned about importing drugs from that third world hellhole, Canada. Without looking anything up, i will guarantee that Canada's safety standards are much higher than ours, so Booker's position is bullshit. And of course the point of this bill isn't to actually do it, but to highlight how ridiculous it is that the same drugs that are sold here in the US are sold in Canada at a fraction of the cost. But i'll remember Booker's explanation the next time a real progressive is lectured about "making the perfect the enemy of the good".