"Climate change is the road less traveled but he's traveled it even more than Al Gore," Graham said. "Al Gore has talked about it and deserves great recognition but he was around here a long time and never introduced a bill."
McCain and Sen. Joe Lieberman, D-Conn., co-sponsored a failed Senate bill in 2003 that would have capped greenhouse gas emissions levels.
Looking ahead to a possible Obama-McCain matchup in the general election, Graham argued that McCain's experience would be a key argument against Obama in a general election.
Noting the experience argument would be more difficult against Clinton, who has been touting the experience she gained in eight years as first lady, Graham argued that Clinton's negatives would help McCain win in November.
"Clinton is a friend, but she is a polarizing figure," Graham said. "She's polarizing and I don't know why but she is."
Bayh said the reason Clinton has high negatives is because "she's been in the arena for a while."
"She was the subject of the right-wing attack machine for all those years and bears some of the scars from that and wears some of them proudly," Bayh said, arguing it is unknown if Obama's candidacy could withstand the "brutal combat" of a general election.
Countering that Obama has "lived a life of challenge," Durbin argued the junior Illinois senator is a "force of nature," and could win in November by winning over new voters, young people, GOP voters and Independents — and inspiring them all to get to the polls.
"He has reached into states Democrats have never seen," said Durbin noting Obama has attracted one million donors to his campaign, many of them low-dollar donors.
But Bayh challenged this argument. "Even with this new force of nature she is within 120 delegates. She must be an impressive force of her own especially getting outspent the way she is."
Bayh argued Clinton's primary victory in Ohio is a "persuasive argument" for why she should be the Democratic nominee.
"[Sen. John] Kerry would have won in 2004 if he won Ohio," Bayh said, "It was the key state last time, she won that state so that's a pretty persuasive argument."
Graham said McCain's path to victory in November includes convincing Independents he will reach across the aisle, as well as relying on the Republican base voters.
"This will probably be base turnout to some extent but I think we all understand that Independent voters are up for grabs and John will try to put states in play that traditional Republicans couldn't," Graham said, pointing to New Hampshire and states on the West coast.
Graham also said McCain will go after Hispanic voters, the vast majority of whom have turned out for Clinton during the primary election.
"He's the one Republican who can go to the Hispanic community and say, 'please listen to my message, I'd like to have your support' and be well-received," Graham said.
The 2008 presidential election may come down to the war in Iraq and Graham argued McCain is going to make his argument that Iraq is the central battlefield for the war on terror.
"He knows war better than anybody running," Graham said. "He is going to campaign on the idea that Iraq is the central battlefront."
Both Democratic supporters argued McCain's support of the Iraq war will hurt him in the general election, with public opinion polls finding most Americans want to see U.S. troops leave Iraq.