In the final days of Germany’s abbreviated election campaign, the task facing its next chancellor has snapped into focus. It appears far more existential, for the country and for all of Europe, than almost anyone initially imagined.

Germany’s coalition government came apart just a day after the U.S. presidential election last November. As a result, a vote that was supposed to come this September is now set for Sunday. German leaders quickly realized that meant their campaign would be largely fought in the early days of President Trump’s second term.

They were nervous from the start. But they were nowhere near prepared.

In just a few short weeks, the new Trump team has cut Ukraine and Europe out of negotiations to end the war with Russia, and embraced an aggressive, expansionist regime in Moscow that now breathes down Europe’s neck. It also threatened to withdraw troops that have protected Germany for decades.

How Germans vote will now be a critical component of Europe’s response to Mr. Trump’s new world order, and will resonate far beyond their borders.

“It is not just another change of government” under Mr. Trump, Friedrich Merz, the leading candidate for chancellor, warned on Friday after taking the stage for an arena rally in the western town of Oberhausen, “but a complete redrawing of the world map.”