WASHINGTON - Wisconsin Sens. Russ Feingold and Herb Kohl endorsed Barack Obama for president Wednesday — a day after the Illinois senator clinched the Democratic presidential nomination over rival Hillary Rodham Clinton.

Feingold campaign field director Paula Zellner also endorsed Obama, wrapping up the three remaining uncommitted Wisconsin superdelegates.

"I've spoken with Senator Obama and made it clear that he could count me as an endorsing supporter of his at the Democratic Convention this August," Feingold said in a statement. "Senator Obama is an effective leader, capable of leading our country into a new era, and I look forward to doing everything I can to ensure his success this November."

Feingold had said he was "inclined" to support Obama after he won Wisconsin's Democratic primary in February. But Feingold held off making the endorsement until now.

In a separate statement, Kohl said "we can unite behind his historic candidacy" now that Obama has clinched the nomination.

"He has worked to restore the trust of so many Americans who are clamoring for a new direction," he said.

Superdelegates are free to vote for any candidate they wish at the convention.

Charles Franklin, a political science professor at the University of Wisconsin-Madison, said many superdelegates had been concerned about backing someone who failed to get the nomination.

"Many were looking for ways to avoid being held responsible for the outcome," Franklin said.