I just had a look and discovered that TER is available again in the U.S. without a VPN? Did they make it available again because of the presidential election?  

Trump vs. Biden.... of course!

...go back to mongering when he's out of office so he signed an executive order overturning FOSTA/SESTA.

and it is because of new. ownership, mostly.

that TER came back online in the US.

I was thinking Truman vs Dewey.

How long was TER shut down?

It was never shut down

None of the reviews of US providers were accessible, whether you used VPN or not, so TER's main function as a review site  for US providers was was not available for 20 months.   For reviewers, all of your own reviews were available to view by going to "My Reviews", but no one else could access them directly.  There were only about 15 posters that remained at various levels of participation on this GD board, usually the most active board on TER.  During the run-up to the 2018 midterm election, the P & R board actually had more activity.  Many other discussion boards on TER went months without a single post.