With now just a month to go until Election Day, the Democratic primary for US Senate in Texas has become so fraught that a TikToker’s accusations have roiled the race and prompted a major endorsement in the backlash.

Former Rep. Colin Allred (D-Texas) criticized state Rep. James Talarico (D) for allegedly referring to him as a “mediocre Black man” and said he would be backing Talarico’s opponent, Rep. Jasmine Croc...