Saying it's time to bury "a dinosaur," two Democratic senators, about to be thrust into the minority, are launching the latest attack on the Senate minority's oldest tactic: the filibuster.

Harkin's plan would still let the minority slow action for up to 25 legislative days. But if the majority fell short of 60 votes on the first attempt to limit debate, it would need 57 votes on the second attempt two days later, until eventually 51 votes could limit debate.

Sens. Tom Harkin of Iowa and Joseph Lieberman of Connecticut began Tuesday what they acknowledge is an uphill fight to revise Senate rules that require 60 of the 100 senators to end debate.