If Trump has a great debate or two and pulls it to a very close race is almost certain to hold NC (GA and AZ) and pick up FL and OH and probably IA. VA and CO appear to be drifting away from the center line and WI, MI and MN aren't likely to be tipping points.
So, once again it appears to come down to PA, NH, NV and ME2. In what order does Trump pick up those states as he gets closer and closer and tips over to a small PV win? I still think that PA flips before all of NH, NV and ME2. Not sure what you count as 'firewall'
If I had to guess, I'd say the PV center line goes through FL, with OH, IA, and NV to the right of FL, and PA to the left. And the rise in PV necessary to flip PA is significant. But at that point the floodgates open rather quickly, with VA and CO falling to Trump as well. (NV->IA->
FL->VA=PA->CO->ME2->NH)
I would define a firewall as a set of states that are held strongly enough to block the establishment of any reasonable battleground strategy by an opponent. I mean, give Trump a 2% or greater lead nationally, and the EVs will come from
somewhere. But we have battleground states for a reason: to provide an electoral path to victory in the event of a close race.
Wait, IA is drifting away? Was there a new poll that showed him ahead by more than 5%? The last two polls (pre-conventions) went to Trump.
Hopefully we'll get more polls soon. This all may be moot, because I can't see Trump getting anywhere near even nationally before November.