First of all you need to prove it would, rather than just assert it, then because this poll was taken very soon after the first sinking of a USN ship in the Mid-Atlantic, dropping the mean number of public opinion to the lowest point yet, but that doesn't mean it would stay there after the heat of the moment passed or that the public would care more if another ship was sunk, because the taboo had been broken already and it just becomes another event in the litany of events in the Atlantic; by this point multiple US merchant ships had already been sunk and the US public was really no closer to joining the war. All they authorized was arming merchant ships.
http://www.usmm.org/sunk39-41.html
16 ships in 1941 alone.
Well, let's see if that checks out... First one I found was asking just a selection of American writers so I discounted it. The second one I found was issued April 28th, 1940:
Would you look at that. Between April 1940 and January 1941, support for entering the war increased by 8 percentage points and opposition declined by 8 percentage points.
8% in 8 year in one poll. Just one with no others from that same period?
So in two years assuming that it was right it had gone from 96% again to 63% against. In the meantime France had fallen and the USSR had been invaded and by the November poll not only had 16 merchant ships been sunk, but a USN vessel had been sunk 1-2 weeks before. If that rate of fall continued in about another 12 months then perhaps it would be 50-50 if more sinkings of USN ships had occurred. Do you really think FDR would go for a DoW with 50-50? I'm thinking he waits until it is 60-40 for declaring war in multiple polls to avoid the political fallout, which puts us well into 1943 assuming that sinkings are even happening at that point and the Brits haven't won the BotA, which I don't think will be the case; in face the better the Brits do in the Atlantic and the more effective they are at defeating the Uboats, the less likely the US public is willing to join the war.
Your certainly not basing that on the previous trends, or anything really, I can see.
Since even after 16 merchant ships sunk in 1941 alone and several Atlantic incidents have already happened the US isn't close to joining the war. That is after the USS Greer incident in September and the USS Kearny being torpedoed in October and several US sailors killed before the Reuben James was sunk at the end of the month. A bunch of incidents happened in quick succession and unless the Uboats started sinking a bunch of USN ships in quick succession it is incredibly unlikely the US is going to be close to getting in the war if they are still 2/3rds against by November 1941 after all of that just happened in a matter of weeks prior.
You're right that public opinion was changing, but it wasn't remotely close to entering the war in a few months anyway given all that had just happened and FDR's unwillingness to risk declaring war without a clear mandate.
Which was a significant change over 1940, when the US wasn't even willing to do a quasi-war. So the US certainly had shifted closer to war by 1941. The next step would be a expansion of the quasi-war to allow American warships to escort convoys all the way across the Atlantic to Britain and possibly even the Soviet Union, which your own link shows majority support existed for. That's going to accelerate the pace of Americans getting killed by Germans and the anger American's will feel with Germany, pushing the US yet again closer to war.
And this is even assuming that the Germans, who presumed war with America as a matter-of-course, don't lose their patience and declare first. And this, in fact, gets back to the OPs question: pretty much any German who bothered to keep abreast of the international situation, from Hitler down to the man on the street, concluded as a result of the lend-lease act that war with the US was imminent (as in, within a years time) anyway. Therefore, the idea that Germany should not have declared war upon the US and said declaration was a mistake is not only flawed in the context of the post-Pearl Harbour environment, but also purely a product of post-war hindsight from the German viewpoint. At the time, the prospect of war with the US was viewed neither with alarm nor with significance by anyone in Germany.
The US was already becoming increasingly aggressive over the course of 1940 and had taken unprecedented action to expand their aid to Britain even in 1939. The USS Kearny was already summoned to aid a British convoy that was being overwhelmed and intruded in a combat zone and got torpedoed with dead and wounded on board, right after that was the Reuben James sank near Iceland, an area already in a declared war zone. As it was in November Congress authorized arming merchant ships, but was no closer to letting warships do full Atlantic convoy runs; they were already enough help getting convoys to Iceland. Again the US public was more than willing to send LL and help the British patrol and fight a quasi war in the Atlantic, but was still an overwhelming majority against declaring war. Multiple incidents immediately before the last poll on the subject including two US destroyers being torpedoed, one sunk, with over 100 dead US sailors still had 2/3rds of the country unwilling to declare war. Again prior to Pearl Harbor isolationists were not about to let the USN do escorts all the way when the RN could handle things on their end, but would let US merchant ships into war zones armed and was willing to let them be sunk without pushing them to war. The public attitude was basically "we're doing enough to help the Allies win, we don't need to actually get into the war; if the Germans want to declare war on us let them and we'll fight, but we won't start it".
The Germans actually were shocked the US was still staying about after the Reuben James incident and were willing to continue the quasi war. The only reason Hitler declared war in December was the belief that once in any war it was only a matter of time before the US declared war on Germany, prior he didn't want to; he felt his hand was forced by the rage the US public felt over Pearl Harbor and how that could be harnessed by FDR (Hitler was a big believer in the shock doctrine: never waste a crisis).
Actually there is no evidence that the Germans felt war with the US was inevitable until Pearl Harbor, they were just pissed about the US actions to aid the Allies, but wanted to keep the US out if possible; inevitability was only felt after Pearl Harbor. In fact the Germans were convinced the Reuben James incident would get FDR his DoW, but when that came and went with barely a response (FDR didn't even make an announcement about it) they felt confident that the US wasn't going declare war any time soon (source is the book I quoted earlier). In the post-PH situation then unless Hitler was willing to effectively call off the Battle of the Atlantic and totally deescalate the situation there there was no chance that the US would stay out as the public was already primed for war due to Japanese actions and any incident would make it easy for FDR to declare war; since Hitler wasn't one to back down, he was probably right that it was better to act first because it was coming due to his inability to step back from conflict. The only reason that the German assessments weren't worried about the US DoW was that they thought it would take longer than it did for the US to make any impact in Europe and would take longer to mobilize than they did, by which time they'd have wrapped up the Eastern Front and be prepared to counter a US intervention. Still they were interested in keeping the US out of the war prior to Pearl Harbor because they didn't want to have to deal with the US if it could be avoided otherwise they would have DoWed the US after LL was passed if what you assert about their beliefs that it was going to inevitably lead to war.