If Tancredo does decide to run, I think he hurts Sam Brownback the most. With McCain, Giuliani and Romney dominating the field thus far, Brownback’s only chance to gain traction is to build rock-solid support among grassroots conservatives, and his current liability among these folks is that he’s perceived [bold mine-DL] as weak on immigration. ~Philip Klein

Mr. Klein’s analysis works pretty well, except for this last part.  Brownback isn’t simply perceived as weak on immigration–he really is, by the standards of a great many conservatives, abominably weak on immigration.  Amnesty Sam doesn’t have a chance as it is.  Tancredo gives social conservatives who don’t want to betray their country an obvious alternative.  Theoretically, Hunter provides the same alternative, but he is even less well-known than Tancredo.