In 1891, Parker participated in the mob that lynched eleven Italian immigrants in New Orleans, in reaction to the murder of Police Chief David C. Hennessy.

[4] Frank P. Stubbs, a businessman and colonel in the Louisiana National Guard, emerged as his chief opponent for the Democratic nomination.

[6] In 1922, he sent the Federal Bureau of Investigation a message begging for help in fighting the Ku Klux Klan, which had grown so powerful in Louisiana that it not only controlled the northern half of the state but had kidnapped, tortured, and killed two people who opposed it.

[10] After his gubernatorial term ended, Parker devoted himself to his experimental farm at Bayou Sara near St. Francisville in West Feliciana Parish.

In June 1929, he was named president of the Constitutional League of Louisiana, which was organized at the St. Charles Hotel in New Orleans to "save the state from Huey Long".

The U.S. Congress gave Roosevelt the authority to raise up to four divisions similar to the Rough Riders of the 1st United States Volunteer Cavalry Regiment and to the British Army 25th (Frontiersmen) Battalion, Royal Fusiliers; however, as commander-in-chief, U.S. President Woodrow Wilson refused to make use of the volunteers, and the unit hence disbanded.