IMO, the US completely flushed whatever chance it had to develop fusion in the 1990's when it dumped the SSC. I know we still have Fermilab, SLAC, and other accelerators operational, but for me, it was a statement that high-energy physics was not something that had full federal support. Private funding AFAIK of fusion is miniscule.
What technical and theoretical issues stand in the way of a sustainable fusion reaction and obtaining electrical power from it that makes it worthwhile?