WASHINGTON (CNN) -- Montana Democratic Sen. Max Baucus called his vote to authorize the war in Iraq a mistake Wednesday and pushed for a phased troop withdrawal from the war-torn country beginning in six months.

Baucus delivered his remarks in an impassioned speech on the Senate floor, only hours before President Bush is set to lay out his new Iraq strategy in a prime time address to the nation. The Montana Democrat had previously remained a supporter of the war in Iraq even as many of his Democratic colleagues increasingly came out against the conflict.

"The administration was not up front with us," Baucus said. "They presented faulty intelligence and inaccurate information about weapons of mass destruction. Unfortunately, the quality of Congress's decision-making was no better than the quality of the information upon which we relied."

Baucus also urged the president not to increase troop levels in Iraq and advocated for a withdrawal to begin by "the middle of the year."

"Throwing more troops at the problem is not a solution," he said. "Escalating the war is not a solution. We must not launch a strategy that has no benchmarks for success. How long and at what cost will we add troops to the conflict? It's a mistake."

Baucus' nephew, Phillip, was killed in Iraq last July.