(CNN)The German election is very much Chancellor Angela Merkel's to lose. But Sunday evening's encounter with her principal opponent -- the sole head-to-head debate of the campaign -- is a moment of potential peril.
German election: Merkel and Schulz to face off in TV debate
Few leaders in the democratic world can match Merkel's experience -- she has led Europe's biggest economy for more than 11 years and polls show her Christian Democratic Union Party (CDU) as the clear frontrunners for the September 24 vote.
There are very few threats to Merkel "sleepwalking" through this election -- as German media puts it -- but this debate could be one of them.
Debating is not Merkel's forte, and her opponent, Martin Schulz of the Social Democratic Party (SDP), is likely to be forceful and well-prepared. He has less to lose -- several polls show him lagging between 10 and 15 points behind Merkel.
Stung by criticism that he is too much like Merkel, Schulz will be trying to set a distinct agenda.
With just one debate scheduled for the entire campaign period, it could prove critical. Around half of Germany's 30 million eligible voters plan to watch it, according to a poll by the Forsa Institute, commissioned by STERN Magazine.
Of those, about 22% said they would likely make up their minds on who to vote for, based on their performance in the debate.
According to Forsa's Peter Matuschek, Merkel's lead over her past opponents has dropped after her debates.
"She is not a good debater, everybody knows this. And that might be an advantage for her opponent if he is in good shape that night," Matuschek told CNN.
Here are three key election issues expected to dominate the debate: