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.