BOSTON — U.S. Sen. Scott Brown has picked up the endorsement of another Maine senator.

Fellow Republican Sen. Susan Collins today called Brown “a refreshing antidote to the polarization that is poisoning Washington.”

Democrats were quick to point out that Brown “canceled out” Collins’ vote in favor of a bill to raise taxes on millionaires – known as the Buffett rule – by voting against it.

The endorsement by Collins comes on the heels of fellow Republican Sen. Olympia Snowe’s decision to back Brown in March.

Snowe, who is not seeking reelection, said Brown is among a dwindling number of lawmakers willing to work across party lines.

Collins and Snowe are considered two of the most bipartisan Republican senators.

Brown is locked in a tight race with chief Democratic rival Elizabeth Warren.