You're theory that Coleman was taken by surprise by Galloway's performance seems ill-founded to me.
In fact, he appeared supremely prepared for the blowhard.
Coleman did not invite Galloway, he granted him his request to appear and he made sure that before he got the mike that a panel of investigators laid out the case.
Hardly the point. In American politics, Perception generally rules the day, and the fact is, the US Senate is woefully unprepared for a HoC style of exchange.
If Coleman was playing for Legalities, it should have been in a less public setting.