I'd add another point, as I mentioned Matthews was going for a "have you stopped beating your wife?" line of attack. The liberal media loves to portray conservatives as intolerant bigots. If Santorum had tried your scenario, I think the exchange would have went something like this:
MATTHEWS
Do you believe Mormons are Christian, Senator?
SANTORUM
It's hard to say because there's different ways people define Christian. Are you going by the premise that Christianity means a belief in the trinity?
MATTHEWS
That's what your church, the Roman Catholic Church teaches, correct?
SANTORUM
Yes. I believe in the trinity.
MATTHEWS
So politicians who do not profess a belief in the trinity aren't Christian in your eyes?
SANTORUM
Well, I didn't say --
MATTHEWS
But that's what your church believes, how it defines Christianity, and you claim obidenence to the Catholic church.
SANTORUM
I do.
MATTHEWS
Are Quakers Christians?
SANTORUM
I thought we were discussing Mormons.
MATTHEWS
We were discussing a belief in the trinity. Quakers do not believe in the the doctrine of the trinity. So your faith tells you that they are not Christians, correct?
SANTORUM
I suppose...
MATTHEWS
And you also believe Seventh Day Adventists are not Christians. In fact, you would say the Christian Science faith founded by Mary Baker Eddy isn't Christian, even though that's the name of the church.
SANTORUM
Are we done yet?
Mormons want Christians to consider Mormons to be fellow Christians. But they do, Mormons will never return the favor.
Yeah, as I said, the forum (i.e., Matthews’ show) does not allow for precise thinking.
Perhaps the best thing to do is not go on there at all. I don’t know why anyone from the right does.