Why did Kennedy do poorly in Ohio?

[🐒Gods of Prosperity🔱🐲💸]

Anti-Catholic sentiment + the state was traditionally Republican at the time

I doubt whatever anti-Catholic sentiment there was in Ohio was greater than in the nation as a whole given the long history of Catholics in the state (typically of the middle class German Republican variety).  It is true that the politics of Ohio were fairly Republican and conservative then.  If you compare the difference between the national and state margin, it's not far off from what it had been in 56.

[🐒Gods of Prosperity🔱🐲💸]

This only proves that Nevada is more reliable than Ohio as a bellwether as it did vote for Kennedy, even when the rest of the West did not (one state by absentee ballots).

Also FDR lost Ohio at one point.

Nevada has been all reliable in every election sans 1976.

Yep, so long as you don't count anything before 1912.