It's also a lot harder, IMO, to convince a top theoretical mathematician to go to NSA vs. remain in public, since there aren't exactly amazing resources NSA can offer (better chalk?), compared to someone who needs access to multi-million or billion dollar resources. In exchange for better chalk (and access to other classified work, sure), you can't publish, so you'll never win a Fields, be respected by your mom, etc. (A guy who really is into nuclear physics could be tempted by DOE, by comparison.)

I think NSA would have a much easier time recruiting "true believers" in US national defense than anything else. i.e. "yes, you're an expert in theoretical math, but rather than doing purely abstract stuff, you can help protect your country from the evil terrorists!". An easier case when the threat was existential nuclear annihilation from a USSR your relatives may have fled in the past, than now where we're going up against mud hut dwellers who can't afford shoes and take over planes with boxcutters.

NSA also does the bullshit "EOE" recruiting, particularly in the high school and undergrad level. Sorry, but most high level math people are not particularly "diverse".

Plus, go to the math department at top universities. Find the US citizen. Find the US citizen who isn't particularly counterculture or does recreational drugs or whatever. Convince him to work for GS/GG wages (maybe $100k, tops?) vs. a tech startup or a hedge fund. With paralyzing bureaucracy, uncertain funding in the next 10-20 years, and stifling work rules.

I would not want to be the NSA's recruiting department.