While the general gist of neroden's post is absolutely correct, the numerical implication is a bit off.
Assuming these estimates of "vaccine effectiveness" are calculated similar to that of the clinical trials, when they say that the vaccine is "64% effective at preventing infection" that means that the if, say, if the overall infection rate is x, then those who are vaccinated will get infected at a rate of 36% compared to those who aren't vaccinated. Even in hotspots, the total rate of infection among the total population is pretty small, so it's not like you have a 36% chance of being infected even if you're vaccinated and unmasked. If the infection rate is, say, 1% of the total population, then an unmasked vaccinated person's chance of being infected is 1% of 36% (0.01x0.36) or 0.0036, or 0.36%. Thus, even if you're not wearing a mask, your chances of getting infected are fairly low. However, bear in mind that 0.36% of 300 million people is almost 11 million people, so even if everyone was vaccinated, a lot of people could still get infected. Even if people don't get really sick, this gives the virus more chances to mutate to new variants that might be more of a problem.
Now I don't have off the top of my head the experimental and epidemiological data that quantify the beneficial effect of mask wearing, but the one experimental study I did read about aerosols suggested that masks reduce the number of aerosol particles roughly 5-fold. (I.e., wear a mask, emit 1/5th the # of aerosol particles). If the reduction in aerosol particles is linearly related to the reduction in infections, then wearing a mask would reduce the infection rate by 80%. This would be .01 x .036 x .2 or 0.000072 or .0072%. This means that the 11 million people who might get infected from asymptomatic unmasked vaccinated people would be reduced to 2.2 million if these people were all masked. (This is not counting the protective aspect that wearing a mask offers to the mask-wearer which also reduces infection rates.)
While this means you don't have a 36% chance of catching the virus if your vaccinated and unmasked, so there's no need to totally freak out about the Israeli reports, it does mean, as neroden wrote, "vaccinated people can be carriers" at a rate higher than previously thought. Thus, we need to do more to break the chain of transmission. One of the best ways to do that is to wear a mask indoors in crowded places, even if you're vaccinated. I would think that being in an Amtrak train would count as being "indoors in a crowded place," especially now that they're selling all the seats with apparently the train consists are still shorter than usual. I'm not sure what the problem is in having a mask requirement as a tradeoff to allow other activities to be able to go on as normal.
As I've said before, I really don't understand why some people are being obstinate about this. Wearing a mask is no big deal. If we really want to go back to "normal" (whatever that is), wearing a mask is something that just has to be done.