Germany’s presumptive next chancellor could be weak from the start, for all sorts of reasons. He didn’t win a particularly high share of votes. Most Germans don’t think he’ll make a great leader. Many of the people who backed his party in Sunday’s elections say they’re not enthused with him, personally.

And yet Friedrich Merz will step into Germany’s top job with an immediate chance to be the most influential German chancellor globally since the financial crisis heyday of his longtime rival, Angela Merkel.

There are two reasons for that. One is President Trump, whose threats to abandon Europe militarily and circumvent it in war negotiations with Russia have given Mr. Merz an immediate foil on the world stage.

The other is the bold, sometimes impetuous, style that has vaulted Mr. Merz to the door of the chancellorship, even as it sometimes alienated friends and foes along the way.

The day after Mr. Merz and his Christian Democrats won a high-turnout parliamentary election and the right to form the country’s next government, the big question in Germany was whether he could deliver the sort of dramatic change that voters said they were craving.

Surveys of people at the polls on Sunday showed widespread national anxieties over the country’s faltering economy, including stagnant growth and a high cost of living, and deep divisions on the hot-button issue of migration into Germany from the Middle East and elsewhere.