Democrats won the Senate races in Pennsylvania,Wisconsin,Michigan,Nevada,Virginia ,Minnesota ,Arizona and Ohio in 2018.
Democrats did better in GA and Texas in 2018 than they did in 2016.
Which are all welcome and positive signs for the Democrats. However the Democrats need to not view 2018 as a barometer for 2020.... and assume the results in these states will lean their way. Mid-term elections when you are the minority party with their associated gains are very different than presidential election years - if the Democrats are magically assuming that the popular vote in these states will look like 2018 rather than 2016 then they have another surprise heading their way.
The Democrats needs to put forward a reasonable presidential candidate focused on a platform of issues which most matter to the voters. A failure to do this will simply lead to four more years of Trump -- at which point the Democrats can only blame themselves ("We are the party that sucks so bad that we lost to Donald effing Trump not once but twice".)