Tancredo just won't appeal to a thrid of the country who believe that there should be no countries or borders. He also probably won't appeal to another third of the country that wants to hire cheap labor without guilt. I'd say, unfortunately, his chances of being POTUS are near zero barring a terrorist nuclear attack in the US.
I disagree with your assessment of Tancredo's chances, at least as regards your one-third, one-third, ratios of voter appeal. How far he could go would depend a great deal, but not exclusively, on how he would or could present himself. I don't think anything like "one-third" of the voting public "wants to hire cheap labor" and a President Tancredo would squelch that---these formulas , I think, are getting a little old and stale, and no issue is ever exactly "either/or". So Tancredo can get pretty far on his own, I think, and would have widespread POPULAR apppeal, but just watch how far the popular appeal would be allowed to go by the GOP Establishment. You thought the Dems were disgusting and pathetic in their attempts to smear Alito? You haven't seen the GOP Machine swing into action to smear Tancredo, who is still nominally, "one of their own".