I think I feel a bit confused with the concept of it being crucial to  "stack a bunch of multipliers." 

Like how would you describe this story: 

A student is planning a career working on US economic policy (because this is something he's had an interest in for a little while). Then, he is exposed to some ideas in longtermism and decides to instead work on AI policy instead (because he thinks it seems like a big deal and is probably more important than economic policy).  

 This feels to me like it's just "one step" or "one multiplier" that puts this student on a much higher EV career path. 

Curious about this part:

“To be concrete, my personal best guess is that >30% of American EAs would have at least a decent shot (say, >20%) of making it into Congress if they chose to dedicate themselves to their local community and spend time practicing the appropriate communication skills.”

Would be curious for a bit more explanation from OP or others on this part.