First, convention bounces have been getting smaller over the last few decades. Since 2004, the average convention bounce has been just 2 points. According to Geoffrey Skelley at FiveThirtyEight, the average bounce during that 32-year period was a little less than 7 points. Even if you assume that President Donald Trump gets the average bounce since 2004 and Biden gets no bounce, Trump won't be close to the lead. It's never gotten higher than 10 points in the average and never below 4 points.

Source: CNN August 15, 2020 12:11 UTC