GOP Sens. Susan Collins, Lisa Murkowski and Mitt Romney have signaled they will likely vote to consider witnesses and evidence.

If all 47 senators who caucus with the Democrats vote to have witnesses and evidence, they still need four Republicans to join them.

The three had nothing to say, substantively, about the first day of the House manager presentation. That’s unlikely to change any time soon, as all three plan to keep their observations quiet until after the presentations are complete.

The question remains: Who, if anyone, is the fourth?