According to a report by "The Economist", at the debate among the Republican candidates for president on February 13, the career politicians verbally assaulted Donald Trump. He is the only anti-establishment candidate who is still campaigning to become the Republican nominee.
Why does the Republican establishment oppose an anti-establishment candidate's becoming president? Here is one reason.
If Donald Trump, the anti-establishment candidate, actually became president, he would install his own set of politically connected men and women in the executive branch. These men and women would be unfamiliar with the members of the Republican establishment, and the consequence is that the establishment members would endure greatly reduced access to the executive branch.
What does greatly reduced access mean? It means that a Republican who transitions from the Republican establishment to a new job as a paid lobbyist would have greater difficulty in arranging a meeting between the attorney of his client (say, a multi-national corporation) and the head of, say, the Environmental Protection Agency. Such meetings are legal and can influence the nature of potential regulation -- in favor of the client. So, if the lobbyist could not arrange such a meeting, then he would receive much lower fees for his services.
The typical fees for successful lobbyists can range from hundreds of thousands of dollars to millions of dollars.
With regards to lobbying the government for high fees, the Democrats and the Republicans are equally dirty. See the political dirt in the reports by The Center for Responsive Politics at OpenSecrets.org.
After the anti-establishment candidate becomes president, his politically connected supporters become the new establishment. They will eventually board the money train for lobbyists. They displace the previous set of dirty politicians on that train. So, why is voting for the anti-establishment candidate useful when we are just replacing one set of dirty politicians with another set of dirty politicians?
It is useful because the anti-establishment candidate's becoming president sends a powerful message: we the voters allow a presidential candidate and his political entourage to become the new establishment (replacing the old establishment) and to board the money train (and earn millions of dollars as future lobbyists) as long as the president actually implements all the ideas and projects that he promised on the campaign trail.
If a president reneges on his promises, then we voters force him and his entourage off the money train.