Why, then, have so few Democrats officially endorsed Sanders? First, because Clinton is extremely popular with both elite and rank-and-file Democrats. Her relative lack of competition is a sign of strength, not weakness — she won the “invisible primary” stage of the campaign. Second, because Democrats are right to be concerned about the general election prospects for Sanders, a 74-year-old self-described socialist. Third, because Sanders’s agenda is hostile to moneyed interests within the Democratic Party.
But if Sanders eventually overtook Clinton, the establishment might resign itself to the prospect of nominating him. There are some loose precedents for candidates like Sanders winning their nominations, especially George McGovern in 1972 and Barry Goldwater in 1964. If you’re going to sacrifice a presidential election — and Sanders would be unlikely to prevail next November4 — you’d at least like to shift the window of discourse in your party’s preferred direction.
A Trump nomination would be more of an existential threat to the Republican establishment. He bucks the establishment’s consensus on issues as fundamental to the GOP as taxation and health care, and he’swobbly on abortion. Splitting with the party on any one of those issues might ordinarily disqualify a candidate. Trump potentially destabilizes the Republicans’ “three-legged stool”: The coalition of fiscal, social and national security conservatives have dominated the party since 1980 or so. But on the issue on which Trump is most conservative — immigration — establishment Republicans worry that he might be so reactionary as to cause long-term damage to the party brand.
Meanwhile, Trump has picked fights with sacred cows like the Club for Growth and Fox News. Most of the conservative media — from the National Review to RedState to Glenn Beck — is anti-Trump.
In certain respects, Trump is engaged in an attempted “hostile takeover” of the Republican Party. Because the downside of nominating him might be so enormous — lasting beyond a single election — the GOP establishment may fight to the death to prevent him from being chosen, even at the price of a brokered convention and a fractured party base.