Even if the polls are really off, Trump is still in trouble

And while Mr. Biden can currently survive a 2016-like polling error, there is no reason a polling error couldn’t be even larger in 2020.

But for now, his lead is large enough to survive a 2016 repeat and just about every general-election polling error in recent memory. He leads by an average of nearly 10 percentage points in national polls since June 1, well ahead of Mrs. Clinton’s four-point lead in the final national polls or her peaks of about seven points in early August and mid-October.

Mr. Biden also enjoys a far wider lead in the battleground states likeliest to decide the presidency. His 13-point lead in a Monmouth University poll of Pennsylvania published on Wednesday, for instance, puts him in a much stronger position than Mrs. Clinton, who had a four-point lead in the last Monmouth poll of Pennsylvania taken just before the election.

Of course, the polls could be even further off this time than four years ago. But there are also many reasons to think they could be better this time around.