"Does the Wisconsin Senate have the power to compel absent Democratic senators to return to the senate floor if they re-enter the state of Wisconsin? Yes."

Says Jim Lindgren:

I would hope that those who rely on the arrest clause of the state constitution would deal with the fact that the privilege against arrest applies “in all cases.” These commentators might try to argue that the drafters of the Wisconsin — and by implication, US – Constitutions meant “in all instances” when they wrote “in all cases.”

As implausible as this interpretation would be in the abstract, in context it would not pass the laugh test. After all, the phrase reads: “in all cases, except treason, felony and breach of the peace.” In context, the framers’ language clearly meant court cases....

That interpretation would conflict with the compulsory attendance provision (Article IV, §7) of the constitution, Lindgren says:

Reading the two constitutional sections together, the courts can’t meddle in legislative affairs by arresting legislators in a civil court case, but each house of the legislature “may compel the attendance of absent members in such manner and under such penalties as each house may provide.”