Wrote last week I thought there was a clear top 2 in the Democratic primary, Biden and Warren, but I had Biden as "1a" & Warren as "1b". Her polling has been strong enough over the past week that I don't think even the 1a vs 1b distinction makes sense; they're co-frontrunners. pic.twitter.com/NM4TC2nNpG

— Nate Silver (@NateSilver538) September 25, 2019