Louisiana Democrats Go Under 50 Percent For First Time In Modern History

Pretty significant. The link below references 1957 as a baseline only because that was when records were kept of such things.(which seems strange)

However it's a safe bet ,since after Reconstuction for a period of 90 years one could have a Republican Convention in a street car ,somewhere in the 1870's to 1880 should be seen as the baseline.

As late as 1978, Democrats made up 90 percent of the Louisiana’s registered voters.
The Brown Pelican has LOUISIANA POLITICS: Democrats Lose Voter Majority–GOP, Others More Than 50% of La. Voters