It's not an official government position that millions of illegal immigrants voted, it's Trump's personal opinion. Much like it was Obama's opinion that Trump would never be President.
Do you see a difference between someone having...
(1) an "opinion" about something that happened in the recent, knowable past -- but which flies in the face of all available evidence; and which, when challenged, you're unable to offer any evidence for -- like for example claiming that "The Kansas City Royals won the World Series last year", or "The Russians were the first to land on the moon", when everyone knows they didn't); and
(2) an "opinion" (i.e. a hunch) about what might happen in some future event -- who might win a football game, or an election, say?
Do you see a difference between someone having...
(1) an "opinion" about something that happened in the recent, knowable past -- but which flies in the face of all available evidence; and which, when challenged, you're unable to offer any evidence for -- like for example claiming that "The Kansas City Royals won the World Series last year", or "The Russians were the first to land on the moon", when everyone knows they didn't); and
(2) an "opinion" (i.e. a hunch) about what might happen in some future event -- who might win a football game, or an election, say?
Or do you think these are basically equivalent?