Look up some of the writing by Rachel Bitecofer. She was the most accurate predictor of the midterms. She predicted something like 42 out of 47 races correctly.
Back last July she said that pick any Democrat and they will be starting with 278 EV. Here is here map:
Wason Center electoral college map
She hasn't seen any change. Her model is based on what she calls negative partisanship. A recent article:
An Unsettling New Theory: There Is No Swing Voter
A re-election of a president is always an initiative on whether the president deserves a second term. If the president is unpopular, the opposition party needs to out up someone less popular to lose. About the only Democrat who could lose this year is Hillary Clinton. The big question for me is how wide the coattails of the Democratic nominee would be. I think Bernie would probably win, but a lot of people who were right of him (about 80-90% of the electorate) would vote Republican down ticket if they voted for him to ensure his more extreme ideas didn't get implemented. With a moderate candidate people see as safe and likeable like Biden (even if many think he's losing his marbles, which I don't see, his aphasia gets worse when he's stressed or tired, but that's a speaking problem, but a cognitive problem) they might be more willing to vote Democrat down ticket because Biden isn't likely going to propose anything the bulk of the population feels is too extreme.
In any case, negative partisanship gets people to turn out to vote who dislike the candidate, or in the case of the midterms wanted to see Trump slowed down. The Democrats have a built in advantage that there are more people who would vote Democrat if you can get them to vote, but the people willing to vote Republican are more reliable voters.
There are many reasons likely Democratic voters don't turn out. In some cases, like 2016, they didn't like the presidential candidate, figured she was going to win anyway, and didn't bother. But a lot of likely Democratic voters also have busier lives (maybe holding down multiple jobs, caring for a family, etc. vs the Republican electorate who has more retired people). Also Republican administrations in many states have made it tougher for Democratic voters to vote. A number of states with Democratic control have made it increasingly easier for people to vote and it has resulted in the states becoming Democratic strongholds.
Barack Obama won in 2008 because a lot of Democratic voters were inspired to turn out and deal with all the hassles to vote for Obama. They didn't turn out in quite the same numbers in 2012, but they did in enough to get him re-elected. In a number of cases it was because Romney with his disconnected air of superiority scared them.
The number of votes cast in 2016 were actually more than 2012 and even 6 million more than 2008 (but the country had 8 years of population growth too). If you look at the demographics of the 2016 vote, there was about 2% more whites than there should have been based on the historical trends. Almost all those extra whites were low frequency white voters who turned out to vote for Trump. It was just enough to push him across the line in Wisconsin, Michigan, and Pennsylvania also thanks to voter suppression and voter redirection efforts in those states. For example the African American vote in Detroit was suppressed thanks to reducing the number of poling places (creating long lines) and disinformation campaigns to get Democratic voters to vote for Jill Stein, or show up to vote the day after.
There are a lot of people who voted for Jill Stein or didn't vote at all who now feel very guilty about it and are determined to vote Democrat this year. There is also a very large number of Americans freaked out about Trump who will crawl over broken glass to vote for anyone with a chance to getting him out of there. A friend of my SO recently confessed to her that she fell for the con and voted for Jill Stein. She's in Florida, so it actually made a difference. She had been silent out of shame for three years.
The 2018 midterms foreshadowed what was coming in 2020. A lot of people who normally don't vote in midterms turned out to vote Democrat and it swept the Democrats into power in the House. In presidential years more Democrats turn out anyway, so the effect may not be as pronounced. Trump has lost a small percentage of his voters from 2016. They have been disappointed and will probably go back to not voting. His rabid base will turn out to vote for him come hell or high water.
In 2016 there were quite a few voters who disliked both candidates, but in many states Trump got the majority of those votes. In the case of negative partisanship, it's better to take a flyer on the devil you don't know than go with the well known devil. About 1./2 those who approve of him will say when follow up questions are asked that they approve of him for economic reasons and not much else. If the economy goes bad, they will stay home, or if there is an attractive third party candidate, they will vote for them. Even if they aren't voting for Biden, their non-vote is a push and Trump is fatally weakened. If you have 100 people, 50 vote for one person, 25 vote for the other, and 25 don't vote, the person who got 50 votes won a 66/33 election.
There are also a number of former Republican never Trumpers who have said they will hold their nose and vote for Biden to get rid of Trump. For them it's a strategic vote, but also a form of negative partisanship. Even if they decide to vote third party or not at all, that still benefits Biden.
Trump's path to re-election was always going to be narrow. It's very doubtful he can break 50% of the popular vote. That leaves him with EV strategies like 2016 without allied governors in Wisconsin, Michigan, and Pennsylvania to help him. There are only a few unlikely scenarios where he could win. On the other hand there are many paths to 270 for any Democratic candidate and several paths to over 300. Democrats have blown it before, so there is no point in getting overconfident, but there is no point in working yourself into an ulcer with worry over the less likely scenarios happening.
If you want Trump gone, vote blue no matter who and anyone who you think might vote that way who is too lazy or too busy to vote, work on them and get them to the polls too.
