Which group blocked the passage of federal anti-lynching laws in the 1920s?

Southern Democrats

Explanation:

The practice of lynching was particularly associated with the murder of blacks in the southern United States prior to the civil rights reforms of the 1960s.

For most years after the secession war, the white majority in the southern United States tolerated and sanctioned terrorist violence against blacks. Licensing was a way of setting terror on African Americans and affirming the superiority of white people.  

The occurrences of lynching were so constant that lawmakers had to intervene and create the anti-lynching laws, but these laws were not applauded by the entire population because Southern Democrats tried to prevent the adoption of anti-lynching laws in the 1920s?

d. it was created with the idea that it could be easily revised if it was ineffective