The Republicans wouldn't nominate Trump, they would be blamed for all the stupid crap he does.
This is the same party that nominated GWB, McCain and Romney. Is this a serious claim? Or just wishful thinking? Literally the best nominee the Repubs have put up in my lifetime was an actor with serious memory recall problems. Even they consider him their high mark.
Your examples actually argue against your point. Unlike Trump, Fiorina and Carson, everyone you mentioned above (including the forgetful ex B-list movie star) were establishment candidates, with prior elected experience and had broad support from party insiders. Now, maybe this time really IS different, but the safe bet is that none of the current three front runners will be able to leverage their current position in the polls to get enough convention delegates to be nominated.
It will be very difficult, as Bush/pubs/Rove/RNC changed their nominating rules when no one was looking in 14. Basically they set it up so that Bush needed only 20% of the voters in primary states to win. It is complicated but a person needs to carry at least 8 states before their name can be entered at the convention for consideration. The Koch brothers are actively supporting numerous candidates at Rove's command in order to splinter the vote. They set the process so that momentum has less impact and big money candidates (Bush the anointed) can slog through the process.
Of course that was all before Trump. Trump may take only half of the initial states and thus be in for a fight till the end with the Bush folks. Other candidates will drop as the process unwinds in the primaries and they will all make Walkeresq speeches supporting Bush. As it becomes more and more likely Trump will not only win the Pub nomination but that he is widely appealing to disenfranchised minority voters, unions and women, the wall street banker folks will simply switch their support to Biden while quietly working against Trump.
You see they don't really care if it is a Dem or a Pub who wins as long as the policy of leaving the working class with a huge deficit while they loot the treasury continues. They do care if Trump wins because he actually says he will tax hedge funds, end offshore tax avoidance and offshoring of jobs, while increasing the cost of US labor. (i.e. he is a main street people's candidate)
Did I mention that Trump is meeting with leaders of the South Carolina Black Business Chamber and Trump also will speak at an event in Columbia, the state capital, hosted by South Carolina's Republican U.S. Senator Tim Scott. Tim happens to be a Black Republican Senator and carries a lot of weight with that demographic in SC. "of the 15 Republican presidential candidates, Trump did best among black Republicans and independents in a Reuters poll."
Trump, in his genius, blew off the Republican sponsored event last week and chose to center himself as the sole Republican courting the black Repulican vote in SC this week. The Pubs just can't figure it out. They gave him tons of media for not attending an event that received not media coverage.
Trump polls better than other Republicans with Hispanic/latinos. Most people have it in their mind that Hispanic is a race (it is an ethnic designation) term. Latinos and Hispanics are actually a very diverse group that includes many races and countries of origin. And yep, you didn't guess it, but many, if not a majority, of legal Latino immigrants are opposed to illegal aliens. Go figure -- they hate crime too and jumped through the difficult proper hoops.
In the post racial USA it appears that the democrats racial polarization may come back and bite them. They could end up losing a significant portion of the black vote.
It is the economy stupid.