[Theoria]

Migration erodes any possibility's of R's winning in the future. Every month, more people become citizens who vote in that manner. Trump will face vast economic headwinds, while Biden can merely promise the moon. This is a similar McCain v Obama situation.

Everyday, more debt will continue to be add to the burden of all. Trump will have to have a message besides blame China. Because, as of now he still is holding to the trade deal, even though they helped to unleash as he put it worse than a pearl harbor situation.

Trump will be the underdog heading up to the debates.

[Lazamataz]

Migration erodes any possibility's of R's winning in the future.

True, but not yet.

Further, Trump seems to have cross-sectional appeal.