A month ago, no one would have ever mistaken Germany’s often taciturn chancellor for an aggressive political campaigner. But prowling the stage in a dark suit and open shirt with a microphone in hand, Olaf Scholz certainly looked like one on Friday night.

At a nearly euphoric rally for someone trailing in the polls, Mr. Scholz spoke for 50 minutes before supporters in Dortmund, one of only two German cities where his center-left Social Democrats are projected to win the majority.

He trumpeted his government’s achievements, like raising the minimum wage and bridging the loss of Russian gas after the invasion in Ukraine. He told the crowd he could still win. And he took a swipe at President Trump.

“If you translate what ‘transactional’ means specifically,” Mr. Scholz said, alighting on a word often used to describe the American president’s approach to politics, “it means I only think of myself and I only do what benefits me.”

Nearly 2,000 Social Democrats jumped to their feet and cheered. “I thought he was in good fighting form,” said Elisabeth Schnieder, 69, who joined Mr. Scholz Social Democrats, or S.P.D., after she retired from her job as a senior care aide.

“I just wish he had shown that side earlier.”

The Friday rally was Mr. Scholz’s last of the campaign ahead of Sunday’s vote. It was also possibly the last of his career.

Mr. Scholz, 66, has been relentlessly optimistic (some might call it unrealistic) in a race that would have seemed hopeless to anyone else. That is because he was the only one who believed he could win in 2021, when his party was stuck at 14 percent before catching up in a few short months to win. That success seems to have inured him against the realities of the polls.

At the same time, Mr. Scholz has clearly relaxed in the final weeks of the campaign. Instead of standing rigidly behind his lecterns at recent televised debates, he leaned against them from the side, in a pose more befitting a 1950s-era Hollywood Cowboy movie than German politics.

It does not seem to have done the job. According to opinion polls, Mr. Scholz’s party is expected to come in with half the support of the conservative Christian Democrats of Friedrich Merz, and also behind the far-right Alternative for Germany.

Sunday’s election was scheduled seven months early because the government Mr. Scholz led collapsed in November. His tenure will likely be cut short by a sluggish economy, a shrinking export market and inane political infighting between the three parties that made up Mr. Scholz’s “future coalition.”

Even some of Mr. Scholz’s biggest supporters were not acting this week like he had a chance to win. The Social Democrats are Germany’s oldest party and have long partnered with organized labor. But this week, one of Germany’s biggest unions called a two-day nationwide public transit strike, ending just over a day before polls open.

Behind all of his bluster, Mr. Scholz and the people around him know that he has in all likelihood lost the chancellorship. His party’s best — and most likely — scenario is a grand coalition, in which the Social Democrats would play a junior partner to the conservative Christian Democrats.

It may spell the end of Mr. Scholz’s political career, but it would put the party in the familiar role of ensuring Germany’s generous social benefits stay intact, even under a conservative-led government.

“It’s the only way we can stop the C.D.U. from rolling back some of the progress,” said Christian Ratschinski, 43, who has been both a machinist and a union member for more than two decades.

Mr. Scholz seemed to hint that such political coexistence was possible, in an unusually friendly debate exchange on Wednesday with Mr. Merz, the man likely to replace him as chancellor.

Asked if he would consider getting on an aircraft flown by Mr. Merz, who is a private pilot and owns a twin-engine plane, Mr. Scholz grinned and nodded. “I’m assuming he has his pilot’s license for a reason,” he said

Mr. Merz’s response came quickly.

“Now you’ll ask me,” Mr. Merz said, “whether I would take him along for a ride.”