Perhaps they were trying to stick to Obama's primary campaign promise of seeking bipartisan cooperation.

Their motivation doesn't enter into it. The argument is about whether they had the power. They clearly did, and they clearly did exercise that power at a later time.

I recall one of the Republicans predicting that at some future time the Democrats were going to regret having used the nuclear option. That time is probably about right now.

I'm afraid there's no way to put that big cloud back into that shiny metal ball.