If you want to conserve anything you have to win. I'm sure Rick Santorum would be the strongest pro-life candidate ever but he can't even win the primaries, forget about the general election. I'm sure Ted Cruz has forgotten more about the Constitution than Donald Trump has ever known. But he's struggling to stay ahead of Jeb Bush in New Hampshire, a state sympathetic to Cruz's Live Free or Die principles.
I don't bash Ted Cruz's principles, I question his political skill. Get a strong, pure conservative nominated and I'll vote for him. If Cruz wins I'll vote for him and put out a giant yard sign.
But in my heart I know Cruz is a long shot, even against Sanders, while Trump is a slam dunk.
I think you are on to something there. On the one hand, Cruz built an impressive ground game in Iowa, but it took a huge effort: He self-congratulated himself on his 12,000 volunteers in IA, and 200,000 nationwide (at least some of whom participated remotely in the IA effort.) Cruz spent a LOT of time in IA (somewhat similar to Kasich' effort in NH.) It's hard to imagine that getting only 4.3 votes per volunteer (counting only the 12,000 volunteers) is sustainable.
However, there may be bigger factors in play. Cruz is a long time politician, and he or at least his staff play that way: The "shaming" mailers in IA, and the gossip-mongering about Carson dropping out are examples. Then, when caught, instead of cleanly putting those things behind him, Cruz tries to lawyer-talk his way out. Supporters excuse the tactics as common politics, but Cruz and his people never seem to quite realize that "business as usual" in politics is a significant part of what many people are fed up with. (That "disgusted" attitude is also a significant component of why so many people don't vote or don't vote often, or if they do vote, figure "they are all crooks or jerks, so I'll just vote for the crook / jerk who'll send me the most $$.) Trump offers these voters an alternative.
Trump plays rough too, in ads and public comments, but falls back on his mostly self-funded campaign to deflect the "typical politician" accusations.
Trump also utilizes a sort of multi-angle bombardment, as we saw last night: He was very gracious to the other candidates in the opening of his victory speech, even while unfurling his new attack ad on Cruz in SC.
Post-Iowa, Trump (with regard to the Carson rumor bit) reminded me of the guy in a movie(?) who walks into a bar, re-instigates a dispute between some hotheads there, and walks out with a couple bottles of booze, as behind him the whole place dissolves into a brawl.