NEWARK, New Jersey (CNN) - If a running mate's chief role in a campaign is to play attack dog, then vice presidential prospect Joe Lieberman's audition is going swimmingly.
The Connecticut senator first questioned Barack Obama's patriotism and bipartisan record on Tuesday morning in Pennsylvania, saying the presidential contest is "between one candidate, John McCain who's always put the country first, worked across party lines to get things done, and one candidate who has not."
McCain's campaign later distributed those comments to reporters.
Lieberman, an Independent senator who caucuses with the Democratic Party, again sounded off to reporters on board McCain's campaign plane during a flight to New Jersey, praising the presumptive Republican nominee's record in the Senate and belittling Obama's.
"In the three and a half years Barack Obama has been in the senate with all respect, there is very little evidence of that kind of bipartisan outreach," said Lieberman.
"Barack Obama talks about bipartisanship," he continued. "John McCain has lived it, worked it, done it. That's why I think in the end, which is election day, which we hope is just the beginning, there are going to be many more Democrats who will vote for John McCain than Republicans who will vote for Barack Obama."
Faced with the V.P. question, Lieberman demurred.
Asked if he would accept a spot on the Republican ticket, he answered: "Uh, where?"