When the Democrats decided to have it their own way, anyway, by filibustering judicial nominations in 2003. They broke with a 217 year old tradition. A tradition is just an unwritten rule. The only thing that enforces an unwritten rule is the respect both sides have for it. Either side has the ability to rewrite an unwritten rule by simply disregarding it. The Democrats chose to do this. They broke tradition. Once a Senate tradition has been broken, the only thing that can bring back the pre-existing Senatorial configuration is for the written rules to be changed to enforce a previously unwritten rule.
The Democrats made a stategic mistake by breaking tradition at a time when the other side possessed the ability to change the rules. Oh, that's right, they thought they were going to regain the Senate in 2004. Haha! Their only hope now is that the Republicans do not have the requisite backbone to change the rules.
I guarantee you one thing, as certain as the grass turns green in Spring, as soon as the Democrats regain the majority, they will change the rules, now that the tradition genie is out of the bottle.
So, Republicans, you have a lot to lose if you don't, and everything to gain if you do change the written rules and enforce the old reality.