By Nick Bryant BBC Washington correspondent

Iron-willed and pugnacious, Democrat Senator Paul Wellstone displayed a passionate intensity that is seldom seen these days in American politics.

Wellstone died in the middle of a hard fought senate race

Rarely was he swept along by the political tide - more often than not, he swam against it.

He was a liberal's liberal, a fierce critic of the Bush administration, especially its policy towards Baghdad.

Only this month, he voted against giving congressional approval to the US president to fight a war against Iraq, even though he faced a tough re-election battle in Minnesota.

'Unlikely figure'

The wrestling champion and former college professor cut an unlikely figure when he first ran for office in 1990.

The son of Russian immigrants, he had never held elective office before and launched an insurgent campaign by driving round Minnesota in a clapped-out bus.

His unlikely victory launched a 12-year senate career, during which became known and respected as one of Washington's most energetic lawmakers.

The 58-year-old died in the midst of one of the most hard-fought senate races of the mid-term campaign, battling to retain a seat which the Republicans have targeted in order to win back control of the senate.

Even in their mourning, the Democrats will have to cast around for a new candidate - and the Republicans face an equally tough dilemma.

Deaths this late in the race often boost the party of the deceased.