They're not really worried about blackmail. This is just an attempt to disconnect the financial aspect of corruption and place it in the realm of moral panic. Probably most of the corruption that happens is between sexless boring ass old fucks. But if they can frame corruption as happening because someone has sex or does drugs, then that gives the larger corruption plausible deniability. "I can't be corrupt, I'm not doing degenerate behavior that makes me susceptible to blackmail!" As if the problem is that people near the top are being coerced into being greedy fucks and not that they willingly do it all the time.

It also lets them spin personal issues as a national security issue, which makes it all of our business. When, in reality, it's not. This is the dark side of the libs trying to get pee tapes for 4 years. If libs make Trump's personal issues a matter of national security, then the right will coop it and do it too. Except that the right is much better at fending off those kinds of attacks than libs are. So it didn't hurt Trump enough but it'll decimate the average Democrat candidate. Or it won't because no average voter actually cares and Democrats are just wasting time on that kind of thing instead of forming a more popular political strategy.