Sen. Ben Nelson (D-Neb.) could decide whether or not to run for reelection as early as next week, he said on Tuesday.

Nelson reiterated his promise that the announcement will come "by the end of" the holiday break, but said that it could come "maybe before then."

The Senate will likely go on vacation after next week.

Democrats have a thin bench in the state, and if Nelson retires his seat could go from a tough battle to a lost cause for Democrats.

Nelson has not yet committed to running for reelection. In recent weeks, a deep-pocketed Republican-affiliated outside group spent large sums on an ad against Nelson in attempts to convince him not to run, and Gov. Dave Heineman (R), who is well-known and popular in the state, said national Republicans had asked him to run, and refused to completely shut the door on the prospect.

But Nelson said that those maneuvers would not affect his decision, calling the ads "silly."

"You can't allow outside groups to influence you as to whether or not to run, whether it's the governor suggesting he might be interested in running or not," he said. "You can’t choose your opponent, you can’t choose your opposition. They're there. You make that decision based upon what you're thinking and what you want to do. "