If Republicans regain the Senate, will they seek to reform the filibuster, sweeping away an obstacle that bedeviled Dems and making it far easier for them to enact their own agenda with a simple Senate majority?

Matt Steinglass argues that the GOP will get rid of the filibuster because unlike Democrats, they’re not skittish about doing what it takes to realize their legislative will. But Kevin Drum makes a strong argument that Republicans won’t take the risk because the GOP’s demographic foundation is deteriorating, meaning it’s only a matter of time until Dems retake the Senate.

I just checked in with Congressional scholar Norm Ornstein, and he argued that there is indeed a scenario under which Republicans would likely target the filibuster.

It all turns on whether Obama wins reelection. If he does, then there’s no incentive for Republicans to go for it, because the Senate GOP’s primary role next year (as it has been) will be to obstruct Obama’s agenda. Filibuster reform, of course, would run counter to this.

What’s more, it would be too risky to junk the filibuster, given the possibility of Dems retaking the Senate with one of their own in the White House. “I could lose that majority, and if I do, the one weapon I’ve got against a Democratic president is the filibuster,” Ornstein explains. “I’m not going to give it up.”

But if the GOP wins a narrow Senate majority and wins the White House, Ornstein says, “they’re going to be strongly tempted to do it.”

The argument against this: If Republicans know long-term demographic shifts are working against them, they won’t risk nuking the filibuster since Dems could quickly regain the majority. But Ornstein argues that the GOP sense of a short-lived majority could actually induce them to take the risk.

“Here is a once in a lifetime chance to implement real revolutionary change, and once we do it it will be years before it can be undone by a Democratic president,” Ornstein says, characterizing likely GOP thinking. “If you believe that Americans will love deregulation and budet cuts once they get them, you’re going to take the big long term hit to get the short term gain.”

The question would then become how they go about getting around the filibuster. Ornstein predicts Republicans might change the rules right up front. Or they could jam a whole bunch of stuff through via the simple-majority “reconciliation” process, such as big tax and spending cuts, repealing parts of health care and Wall Street reform, and reinstating any defense spending cuts mandated by the failure of the supercommittee. After that they could pursue changes to the filibuster via an array of other procedural tactics.

So Dems: It could happen. It’s yet another way the stakes of this presidential election are extraordinarily high.