ATLANTA — Plans for the final debate of Georgia’s raucous race for governor collapsed on Wednesday after the Republican nominee, Brian Kemp, abandoned the forum’s long-scheduled timing so he could campaign alongside President Trump this weekend.

Mr. Kemp had been expected to meet Stacey Abrams, the Democratic candidate, in a Sunday evening debate that was announced in September and was to be broadcast live. But Mr. Kemp backed away from the 5 p.m. debate in Atlanta after Mr. Trump’s campaign set a rally in Macon, about 100 miles to the southeast, for 4 p.m.

The upending of the debate calendar set off an hourslong quarrel that seemed likely to reverberate and resurface through the final days of an election cycle that was already acrimonious. By the time trick-or-treaters were knocking on doors on Wednesday evening, Mr. Kemp had agreed to a different time for the debate — 7:30 p.m. on Monday, the night before the election — but Ms. Abrams’s campaign balked at altering the terms of a debate that were set more than seven weeks ago.

“We believe it would be irresponsible to break our commitment to accommodate his failures,” Lauren Groh-Wargo, Ms. Abrams’s campaign manager, said in a statement on Wednesday night. “We refuse to callously take Georgians for granted and cancel on them. Just because Brian Kemp breaks his promises doesn’t mean anyone else should.”