Reagan Won in a Landslide?

 No, Reagan didn't win the election of 1980 in a landslide, or even close to it.  But he governed as if he had won the mandate conferred by a landslide.  

There were three main candidates in 1980:

Jimmy Carter, incumbent, got 35.5M votes and 49 electors.

Ronald Reagan got 43.9M votes and 489 electors

John Anderson got 5.7M votes and no electors.

Anderson was a moderate republican, a thing which no longer exists.  In hindsight, it's pretty clear that he ran as a spoiler, stealing votes from Carter.  In addition to the third party candidate, Reagan's team sabotaged the hostage negotiations with Iran, getting them to defer the release of the prisoners until shortly before the inauguration.  Reagan took credit for this, even though it was entirely the work of Carter's team.

Before this sabotage occurred, it looked like Carter had a solid path to re-election, being up by as much as 15 points over Reagan.

Carter won only 6 states: Hawaii, Maryland, Rhode Island, DC, and his home state of Georgia and his running mate's home of Minnesota.    But many of the states that Reagan won were flipped by Anderson's cut:

Reagan won Arkansas bu 5,000 votes.  Anderson got 22000.  6 electors.

Reagan won Connecticut by 135000 votes.  Anderson got 172000.  8 electors.

Reagan won Delaware by 5500 votes, Anderson got 16000.   3 electors.

Reagan won Kentucky by 19000 votes.  Anderson got 31000,  9 electors

Reagan won Maine by 17000 votes.  Anderson got 53000.   2 electors.

Reagan won Massachusetts by 4000 votes.  Anderson got 382,000.   14 electors.   (This is where I was living in 1980)

Reagan won New York by 170,000 votes.  Anderson got 468000.   41 electors

Reagan won North Carolina by 40,000 votes.  Anderson got 53000. 13 electors.

Reagan won Tennesee by 4500 votes.  Anderson got 36,000.  10 electors.

Reagan won Vermont by 12000 votes. Anderson got 32000.   3 electors.

Reagan won Wisconsin by 107000 votes.  Anderson got 160,000.  11 electors.

All together, Anderson took at least 120 electors from Carter.   this was not enough to overturn the election: 369 to 169 electors.  Reagan won.  but where the pundit class tells us it was a landslide, it was actually a fairly near thing.

Reagan proceeded to sabotage the income tax, unions, monopoly regulation, infrastructure construction and much more, and we have still not been able to recover to this day, more than 40 years later.