[DennisP]

And despite that, the fusion triple product, which has to get above a certain threshold to achieve net power, advanced exponentially from 1970 to 2000, and in 1999 a reactor in Japan got results with deuterium fuel that would have exceeded breakeven had they been using D-T.

Then governments decided to put most of the fusion money in a three-decade construction project in France, cancelled a bunch of projects, and progress slowed.

At least private investors are starting to pitch in; Tri Alpha just got $500 million, General Fusion has a fair amount, and YCombinator invested a little in Helion.