One of the odd features of the 2016 national election is that Hillary Clinton's entire campaign (from her to the PACs) went through $1.2-billion (NY Post numbers). Donald Trump? He spent approximately half that amount.
Up until this election, it was accepted that money mattered and the higher spender.....generally won.
So the question to ask....does it now make any difference?
Some people will say that a fair chunk of the money goes to polling....to tell you where the people stand in various states....on various issues. Yet in the 2016 case, the polling people failed....miserably.
In the 2020 case? One might look at this campaign as a Trump adviser and suggest that real campaign money be centered on the thirty states that he won, and to a much lesser degree on the next five states where he came fairly close....basically forgetting about California and NY entirely.
So Trump could under-spend again (say fifty-percent of what a Democratic candidate would spend)? Yes, and here is the bolder statement....it's pretty good odds that only marginal candidates will primary against Trump in the GOP primary.....so he won't have to spend more than forty-million flying around the US to speak at a once or twice a week campaign rally during the primary.
Clinton spent, with her money, DNC money, and PAC month....near $750-million. I have my doubts that Trump will even spend one-third of that amount in this 2020 election.