General Discussion

Mondale didn't win a single state west of the Mississippi, Hart won all the states west of the Mississippi.
Mondale and Hart each won 26 states.
Mondale won 38.3% of the vote, and Hart won 35.9% of the vote
So, Mondale's lead over Hart going into the 1984 Democratic Convention in San Francisco was less than 3%.
The Democratic Party was a divided party, between Mondale supporters and Hart supporters (who were mostly young voters)
If Mondale had selected Gary Hart as his running mate instead of Geraldine Ferraro, he would have essentially "united" the two factions and a united Democratic Party might well have defeated then-President Reagan in November.

So, Reagan getting 62% of the vote in the general election was likely the result of a divided Democratic Party.