U.S. Senator Paul Wellstone ? a standard bearer of the liberal wing of the Democratic Party in American politics ? was killed in a plane crash Friday, in the midwestern state of Minnesota. The senator?s wife, Sheila, and his daughter, Marcia also died in the crash ? along with three campaign workers and two pilots.

The plane went down in light snow and freezing rain near the town of Eveleth in the northern part of Minnesota. Senator Wellstone was locked in a tight race for re-election, with the mid-term congressional elections just two weeks away.

In Minneapolis, campaign manager Jeff Blodgett confirmed the crash to reporters.

?When the senator?s plane was late we were in touch with our people who are at the Eveleth airport. They reported that their had been a plane crash. It became clear after a while that it was the senator?s plane, and so we are all obviously completely stunned and shocked and grieving.?

Appearing at a news conference with visiting Chinese President Jiang Zemin, U.S. President George W. Bush expressed his condolences to the senator?s family, friends, and constituents.

?Paul Wellstone was a man of deep convictions. He was a plainspoken fellow who did his best for his state and for his country. May the good Lord bless those who grieve.?

In Washington, flags at the Capitol flew at half-staff. Senate colleagues paid their respects at Senator Wellstone?s office.

?He was a man of enormous ability, but most of all he was a caring person.?

A 58-year-old former college professor and the son of Russian immigrants, Paul Wellstone was first elected to the Senate in 1990. He was a passionate liberal, who fought for expanded social programs. But he often worked on specific issues with some of the Senate?s most conservative republicans.

The cause of the senator?s plane crash was not immediately known. The U.S. National Transportation Safety Board is investigating.