The U-S Senate today will debate two plans that would add a prescription drug benefit to Medicare. One of the plans is co-authored by Iowa Senator Charles Grassley along with two other Republicans, three Democrats and the Senate’s only Independent member. Grassley calls it “tri-partisan.”Grassley says his bill doesn’t break the bank like the Democrat plan does. He says it uses competition to drive down the high cost of prescription drugs.Grassley, though, believes neither his plan nor the alternative will be able to clear a parliamentary vote today in the Senate, stalling the issue indefinitely.