This graph is fascinating in looking at Biden’s poll gap compared to Clinton’s in 2016.
Clinton in 2016 started off well ahead of Trump but actually fell behind him for a brief period. She rebounded at the convention to a 7% lead but then declined to a 2% lead, rebounded to 7% and then in the final days dropped to a 4% lead in the polls (she won popular vote by 2%).
Biden’s lead has moved around a bit but been between 7% and 10%. The good news for Trump is that Clinton was also once 7% ahead, but Biden’s lead is far less volatile.
The conventions this year will have less impact as they are virtual. Probably fewer campaign rallies also. So the debates are likely to be the events that could most change things.