The news footage has become grainy with age but is no less vivid: Helmeted Chicago police in a haze of tear gas flailing with billy clubs at demonstrators, while inside a hall politicians hold ugly shouting matches over the bloody battles both on the streets outside and half a world away in Vietnam.

The Democratic National Convention in Denver this week comes exactly 40 years after that jolting episode that became a milestone in American politics.

While another unpopular war, this one in Iraq, will take center stage at the 2008 convention — in which Barack Obama is expected to be nominated in what amounts to a party group hug — it will look nothing like the one in 1968 marked by violence and deep party dissension.

Thousands of protesters are expected in Denver, including a group called Re-create 68 that leaves no doubt where its inspiration lies. One group even says it will use mental energy to shake the Denver Mint and shake the money out. But while there are plans for scores of demonstrations and anti-war rallies, and members of an anti-abortion group will try to be arrested, the incendiary rhetoric has been toned down and no repeat is expected of the violence that plagued the 1968 convention.

Much of what will happen — and won't — starting Monday is a direct result of what unfolded four decades ago.