FiveThirtyEight has Biden with a 70% chance of winning at this point and I think that is a fair assessment. The polls have been extremely steady with hardly any convention bounces and a much smaller “might change their mind” crowd than usual. Third parties will also have no effect on things in the Presidential race as the public spirit that drove people’s interest in third party Presidential candidates mostly disappeared during the Trump Presidency (still a strong public belief in the value of third parties for lower offices though - and hence my concentration on party building at the local level). Remember, if the polls stay steady, then that 70-30 chance of winning for Biden will grow to 80-20 and then 90-10 as the election grows closer and Trump runs out of time to change things. So where might this apple cart be turned?
The first part of that 30% potential for Trump to win then comes from changes in opinion that might happen, for example, with the debates - and I don’t see a particular advantage for him there (my opinion - not evidence based)
a second part of that 30% potential for Trump comes from turnout issues and the supposed enthusiasm gap. Including PACS there will be about $4 billion spent on the Presidential election - probably half to 2/3 of that in negative ads trying to dishearten opponents voters and lower the turnout. Right now Biden’s voters are just as enthusiastic about voting as Trump’s voters (it’s just that they have enthusiasm about voting against Trump rather than enthusiasm about voting for Biden). So the question here is whether negative advertising affects one type of enthusiasm differently than another type of enthusiasm. I haven’t seen any evidence that it does.
a third part of that 30% potential for Trump’s to win is in the idea that Biden just can’t hold it together and will play it overly safe and his lead will slowly deteriorate until he loses in a Clintonesque manner. Personally, I thought Biden was going to collapse back in January - but his campaign staff and the full force of the establishment corporate Democrats have done a marvelous job of propping him up. The pandemic thus helps Biiden a good deal as he can make scripted pronouncements from his basement, talk about his family tragedies with talk show hosts, feed the media with statements about having empathy and providing a return to a more normal and less dramatic Presidency (his only real campaign message), and generally wait out the clock until election day.
a fourth part of that 30% potential for Trump to win comes from the likelihood that he will throw out a variety of October surprises where Biden might have a difficult time refuting before the election - but I’m guessing they will be hard for the public to differentiate from all of the other crap being thrown out.
a fifth part of that 30% potential for Trump to win is with a contested election that comes down to who has the better lawyers (i.e. the George W Bush route to victory). With the full force of the Attorney General’s office behind him and a strongly conservative Supreme Court - the Biden campaign has to rely on good outcomes at the state court level that are upheld in the Federal courts. The Republicans will be contesting a huge percentage of votes in every swing state and the state-by-state rules for provisional ballots will become crucial. Thus, this factor leads me to look at data on control of State Supreme Courts in swing states. Michigan & Wisconsin & Arizona & Ohio have Republican leaning courts while North Carolina & Pennsylvania are currently Democrat leaning. So the edge on this factor goes to Trump.