Lieberman is an independent senator from Connecticut who was the Democratic vice presidential running mate to Al Gore in 2000. This year Lieberman is supporting Sen. John McCain, R-Ariz., for president.
Tuesday night, Lieberman told delegates at the Republican national Convention Sen. Obama, D-Ill., has not reached across party lines to achieve anything significant in the U.S. Senate.
Gibbs called that "a lie," noting Obama worked with Sen. Richard Lugar, R-Ind., to keep nuclear weapons from terrorists and with Sen. Tom Coburn, R-Okla., on the federal budget.
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