Former Rep. Rob Portman’s (R-Ohio) Senate campaign is up on the air Tuesday with a new ad that labels cap-and-trade “a job killer for Ohio.”    

In the 30-second spot, Portman warns that a carbon tax could cost Ohio some 100,000 jobs.

Portman’s Democratic opponent, Ohio Lt. Gov. Lee Fisher, has also raised concerns about cap-and-trade. Fisher wants changes to the bill currently before Congress.   

Ohio Democrats quickly hit back Tuesday on Portman's ad, claimed Portman embraced cap-and-trade as a member of Congress. Here's what Portman wrote in 1996: "Private sector incentives, such as permitting companies to trade discharge outputs, can both reduce pollution and costs. If we can harness the power of market incentives, we'll do more with less."

In response, Portman's campaign said endorsing "incentives" is not the same as mandating caps, which the bill currently before Congress proposes. 

In Pennsylvania’s Senate race, the differences on the issue are sharper. Former Rep. Pat Toomey (R) released a Web video Tuesday hitting opponent Joe Sestak’s stance on the cap-and-trade bill. Sestak voted for the measure in the House.      

Congress left for its July 4 recess with a renewed sense of pessimism on cap-and-trade. Lacking GOP support in the Senate, Democratic leaders openly said it’s unlikely they will find 60 votes in the Senate for a tax on carbon emissions this year.  

-Updated at 5:45 p.m.