WISMAR, Germany—Candidate Georg Pazderski of the anti-immigrant Alternative for Germany spent nearly half his speech in this harbor town earlier this week highlighting the danger of Islamist terrorism. Chancellor Angela Merkel dispatched the topic in roughly 80 seconds in an address here the next day.

As this country’s election campaign reaches its crescendo ahead of Sunday’s vote, its participants appear to be fighting different battles. Ms. Merkel, looking assured of victory, is engaging her opponents in mainstream parties...