First, from the ABC/WaPo poll a week ago to this one, we've gone from Clinton +4 to Clinton +12. Now, you note, one is ABC/WaPo and the other is ABC. From what I can tell, this is the same polling shop (Langer Associates) moving from a standalone poll to a tracking poll for the final two weeks of the cycle. For whatever reason, ABC is the lone sponsor without The Washington Post.
Here's the current PollTracker Trend Chart since June ...
On it's own an 8 point move in one week and a 12 point overall is a pretty big deal. But that number is actually not that out of line with other premium phone pollsters who sample landlines and cellphones. We've had a number of recent polls in the high single digit or 10 point range. The bigger deal is why. The blizzard of sexual assault and groping accusations against Trump have driven Clinton's margin among college-educated white women to an almost unbelievable 32 point margin. Over all Trump leads with white voters by only 4 points; Romney's margin was 20 points at the same time for years ago. Trump's 'rigged election' claims and especially his refusal to say he will accept a defeat on November 8th have generated an overwhelmingly negative response.
But here's the key, the big deal ...
The previous ABC/Post poll found a sharp 12-point decline in enthusiasm for Trump among his supporters, almost exclusively among those who’d preferred a different GOP nominee. Intended participation now has followed: The share of registered Republicans who are likely to vote is down 7 points since mid-October.
Clearly a significant part of the move from a 4 to 8 percentage point lead for Clinton is a significant number of Republican voters dropping out of the likely voter pool. They appear to be concentrated among non-Trump Republicans who came around to Trump after he won the nomination. Where this matters is not so much in the presidential race - where a Clinton victory seems increasingly likely - but down-ballot in Senate and House races. I'm not sure I've ever seen a drop off in likelihood to vote which is so rapid and so soon before an election. To be fair, this isn't really a number I'm even used to looking for. You don't usually have sharp drop offs like that before an election. People on both sides tend to get more pumped up, more driven to partisan affiliation. Usually you are looking at who's getting their voters more activated.
Yesterday I mentioned the mix of reasons why I think Democrats may over-perform expectations in the Senate. If something like what this poll says is happening bears out, I think that gets you close to what might be a genuine wave election. Again, one poll, a very weird cycle. I'd take nothing for granted. But it's a hint of a perfect storm type scenario. Polls over the next few days bear close watching.