• Update: Brian Kemp won the runoff on Tuesday night.

• Get Tuesday’s full results here.

ATLANTA — Georgia Republicans will pick their nominee for governor in a primary runoff on Tuesday, choosing between two longtime public officials who have been jockeying to prove their conservative bona fides and their fidelity to President Trump.

Polls will close at 7 p.m. Eastern. Here’s our guide to the race:

Why is the race close?

Although Lt. Gov. Casey Cagle was the far-and-away first-place finisher in the primary’s initial round of voting in May, he wasn’t able to avoid Tuesday’s runoff against Brian Kemp, Georgia’s secretary of state.

Mr. Cagle’s campaign has mostly skidded since, with his bid heavily damaged by the revelation of a secretly recorded conversation in which he said the Republican primary had become about “who had the biggest gun, who had the biggest truck, and who could be the craziest.” Mr. Cagle was also recorded acknowledging that, in an effort to thwart a rival’s fund-raising efforts, he had supported a measure that he judged to be poor public policy.

A real estate deal of Mr. Cagle’s has also brought scrutiny.

Mr. Cagle tried to repair some of the damage last week by rolling out the endorsement of Gov. Nathan Deal, who is popular in his final year in office. Two days later, Mr. Trump threw his support behind Mr. Kemp, who appears to have gathered substantial momentum in recent weeks and has described himself as “a politically incorrect conservative.”