So many smart people I know are convinced that presidential campaign ad spending operates in a terrain of sharply diminishing returns, but I think the best evidence says otherwise.

Trump won despite a large financial disadvantage in 2016, which leads some people to dismiss the significance of the fact that he'll be much better funded in 2020 but that's probably wrong and it'll help compensate for some of his current struggles.

And part of what happened in 2016 is that Clinton's spending strategy was too aggressive relative to the Electoral College. The money helped her win votes, just not necessarily the votes she needed.