Your reply caused me to visit Andrew Sullivan's bio page.
Where, sure enough, I found...
In his summers, [Sullivan] interned...at the Centre For Policy Studies, Margaret Thatcher's informal think-tank, where he wrote a policy paper on the environment, called 'Greening The Tories.'
Which might make him a Thatcherite. Or, given the slant, it might not...
And, Thatcherite-or-no, I wonder how a conservative would become the editor of The New Republic. Was it not a more-or-less leftist journal when he ascended in 1990-91?
And, perhaps I am mistaken, but I seem to recall Sullivan himself describing his views as "liberal" when he came to the country. When he turned on Clinton, it was "news", was it not?
I don't dispute your assertion. But I still can't clearly determine whether Sullivan's career migrated to the right or started on the right.