WÜRSELEN, Germany — What happened to Martin Schulz?

Mr. Schulz, 61, the candidate of Germany’s Social Democratic Party, was once the only person who had a real chance of taking the chancellorship from Angela Merkel after nearly 12 years.

He had left his job as president of the European Parliament to take her on. He won his party’s backing in March with 100 percent support. Some early polls had him beating Ms. Merkel. The German news media called the sudden burst of enthusiasm the Schulz effect.

Fast forward, just days from the Sept. 24 election, and that hype has fizzled. Ms. Merkel’s party leads Mr. Schulz’s Social Democrats 36 percent to 23 in the latest polls. No one gives him even an outside chance of winning.

Many, even within his own party, say Mr. Schulz became a victim of overly inflated expectations and tactical missteps. But there has also been a larger problem for his party — having its independent voice and identity subsumed after joining a coalition dominated by Ms. Merkel’s Christian Democratic Union, or C.D.U.