TD - I agree. If belief in the Trinity is crucial for salvation - as most bible-believing xtians assert - it ought to be possible to explain it to your granny.
If somebody can only state something by contradicting yourself or committing a heresy or using esoteric Greek terms - the meaning of which 99.999...% of xtians don't understand - then it ought to be obvious they are defending the indefensible.
Christianity is a polytheistic religion.