I'm often amazed at the fake news agenda and the attempt to portray a national poll, which would lead you to certain false beliefs.
If you go back to the 2016 Presidential election....just over 52-percent of the general public showed up to vote (that in itself says a lot). But here's the real substance to look upon....thirty states came to vote for Trump....only 20 states for Hillary Clinton.
If you go and do polling of the 30 states, I'm willing to guess that virtually all of them are still in some positive trend for Trump today, and will likely be that way in 2020.
So, only the thoughts of 30 states matter? Yes, that's basically the whole story. It doesn't matter if 90-percent of California or New York go another direction....those thirty states hold the electoral power over the remaining twenty.
What also falls into the 2020 election? There's this odd 2018 senate race going on in Michigan....with 'Kid Rock' now announced as a GOP candidate. He'll have to run against a Democratic senator who has been there three times now and won. The influence of 'Kid Rock'? He'll draw the youth vote and some of the Detroit votes, along with the GOP. For 2020, Senator Kid Rock (assuming he wins in 2018) will be a major cog in getting Michigan again in the win-column.
If the GOP wins another three Senate seats in 2018? It puts the polling back into the thirty-state equation, and you can basically discount whatever the Hillary states of 2016 say or think. You could easily have another case where one or two million votes do appear for the Democratic challenger to Trump, but not enough to affect the thirty-state count.