I was able to import this one, thanks! (And I was able to independently verify that it's ThomasV's key).
Then, however...
In that procedure, at this step...
Download the Electrum image file and the associated signature file. Open a Finder window, navigate to the location where you saved the Electrum .dmg file and the .asc signature file, and double click the signature file.
...all that happened was that it imported the key (again, with no apparent harm). What did
not happen was what the procedure said would happen:
Mac GPG will launch the verification tool, and compare the .dmg file to the signature file. Once the verification tool has completed its diagnostic it'll pop up a [results window].