Biden has been doing well in the polls, both national and state-level. Indeed the latter polls suggest Biden may be running even farther ahead nationally than we thought. That is Harry Enten's argument in his latest CNN column.
"One of the big questions when we look at national polls is whether or not they're an accurate representation of what is going on at the state level. One of the easiest ways to check is to compare state poll results to the past presidential vote in a given state. I did so for all telephone polls that called cell phones since the beginning of April.
When we average out these state polls, they suggest that Biden's running about 6 points ahead of Hillary Clinton's final margin.
In other words, the state level polls suggest that Biden has a national lead of around 8 points.
That's actually a little greater than the 6.6 points Biden has in the high quality national polling average taken during the same period....
Additionally, we can look at states we expect to be at least somewhat competitive (i.e. those where the margin was within 10 points last time) and those that we don't think will be close in 2020.
In the competitive states (where most of the state polling has been conducted), there has been an average swing of 6 points toward Biden compared to Clinton's 2016 result. The same is true in the non-competitive states....
At least from this state level data, it does not seem that either candidate is running up the score disproportionately in areas that were already friendly to him....
We can test our data, too, to see what would happen if the polls are underestimating Trump like they did in 2016.
What I found was Biden would still be ahead, even with a 2016 sized mishap.....Concentrating on just the competitive states, the polls undersold Trump by 2 points (RealClearPolitics) or 3 points (FiveThirtyEight). If the polls in the competitive states were off by as much as they were at the end in 2016, Biden would still be ahead in states like Florida, Michigan and Pennsylvania."
The latter is a key point. At the moment Biden is running far enough ahead that even if the polls were off in a similar way to 2016, he would still win the electoral college.
I would also add the Enten's higher estimate of Biden's national lead is consistent with the lead we are seeing in the 85,000+ interview conducted by Nationscape since the beginning of the year.