Mitt Romney told Republicans not to vote for Trump. He ridiculed the candidate for whom many of them had voted. He said that "Trump was playing them for suckers". The "suckers" have responded. There have been numerous rallies in support of Trump and full of outrage against Romney who they view as part of the Republican establishment that they detest. They don't believe that they are suckers and they don't know why Republican leaders will not accept the outcome from the democratic process. One Trump supporter stated that Trump is the "voice of the people".
Many Republicans praised Romney for attacking Trump and the ideas that he has articulated. Like Romney, they don't accept him as a "true conservative" or a "real Republican. On the other hand, Trump has been defeating establishment candidates in the primary campaigns. He is the voice for a large segment of the Republican Party. Some of them would like Trump to take over the Party.
Trump may not be able to takeover the Party whose leaders are trying to expel him but the Republican Party is clearly a splintered Party. Many of their leaders, like David Brooks, have raised concerns about the future of the 150 year old Republican Party. Trump's success with a significant number of Republicans indicates that the Party does not represent their interests. They once called establishment Republicans RINO's or Republicans in name only. Now establishment Republicans reject their leader as a real Republican. The Republican coalition that was carefully developed with Nixon's Southern Strategy has reached its end point. We have more than one Republican Party.
The Democratic Party under Roosevelt, and until Lyndon Johnson pushed the civil rights bill through Congress, functioned as a coalition between "Dixiecrats" in the South and Democrats in the rest of the country which was heavily influenced by organized labor. The Dixiecrats had no interest in the Party of Lincoln. They joined forces with the Democratic Party. They were able to moderate some of the liberal programs that they did not like, and they were a powerful force on national defense. A large portion of the defense budget was used to develop the South economically. The passage of the Civil Rights Bill ended the alliance between the Dixiecrats and the Democratic Party. Richard Nixon took advantage of this rupture and managed to turn the Dixiecrats into Republicans. What was once the "Solid South", that always voted for Democrats, became the "Solid South" that always votes Republican. The rise of Donald Trump may rupture that alliance. It would be similar to a situation in which the Dixiecrats tried to take control of the Democratic Party. The historical roots of the Republican Party are not in the South. It has been the Party of business, and it was very successful in the agricultural states. The business community has evolved culturally along with the globalization of the economy. Most multinational corporations get half of their income from their foreign subsidiaries. They are as multicultural as they are multinational. They also require a sophisticated and well educated workforce, and a government that can work with them to build international alliances. Trump's supporters have been left out of that process along with many traditional Democrats who have not prospered under globalization. Many Democrats who have also been left out of that development voted for Trump in the Republican primaries that allow independents to vote. Both parties are dependent upon the votes of Americans who feel that they have been left behind. There is room for a Populist Party which reflects their interests. The two party system in America may not have a big enough tent to include all of them. Trump has stretched the Republican tent to a breaking point. The arch conservative business wing of the Republican Party has depended upon the Trump voters to protect their interests. The Republican Party has been able to satisfy their desire for tax cuts and and a more friendly regulation of the economy. It cannot continue to do so without the votes of Americans who have responded favorably to Trump's demagoguery.