They don't have the votes to block an additional $2 billion for the popular program. Many have heard from car dealers back home.
Clunkers must be crushed or shredded within 180 days, whether all usable parts have been salvaged or not.
If Americans continue reaching into their pocketbooks, back-to-school sales could be better than expected.
Americans participating in the 'Cash for Clunkers' program are buying new cars that get, on average, 9.6 miles per gallon more than their trade-ins.
Fuel efficiency requirements for new cars bought under the rebate program aren't strict enough, say some.
GM, Chrysler saw smaller declines in sales in July. Ford, Subaru, and Hyundai, meanwhile, registered actual sales increases compared with a year ago.