Can I visit the US twice within a 90 day period under the Visa Waiver Programme? 2nd time is only to transfer (change terminal, not airside).
VWP doesn't have a "so many days in so many other days" thing like the EU 90/180 rule. Every entry, you get to make your case to the Immigration Officer as to why you should be admitted. You can come every weekend if you have a reasonable reason that makes sense to the officers and doesn't seem to conflict with US immigration law or policy.
In your case, you'll want to have your onward transportation departing the United States, and it wouldn't hurt to have some proof of a bona-fide activity in that destination country.
And as always, it helps to have proof of "ties to home country" and "adequate funding for trip" and all the usual things they want to see to know that you're not likely to remain illegally.
Also in your favor is that you were admitted under VWP before, and that your previous stay was uneventful.