"How is the adversity supported by facts rather than emotional rants."
Until someone actually does something all fear is based on emotion and beliefs of what "might happen" if such a candidate were elected.
Naturally it's easier to understand why many Democrats would be against him based upon his own words or promises.
He plans to repeal Obamacare, deport 11 million people, tear up the Iran deal...etc Clearly those acts oppose the Democrat's agenda.
However the Republicans fears are more nuanced. Many consider Trump to be a RINO (Republican in name only).
They don't consider him to be a "true conservative" based upon his past stances as well as his recent mention of being in favor of a (single payer health insurance system) which goes a lot further towards socialist medicine than Obamacare.
They also fear that he will "work with Democrats" to negotiate deals rather than attempt to destroy their agenda. They don't want a candidate to compromise. Others feel he's making promises which cannot be kept simply because of the nature of how government power is divided.
An entrepreneur can fire people who disagree with him.
You can't fire congress for opposing you or creating gridlock.
Last but not least since he is self funded he is not beholden to the billionaire donor class or any self-interest groups which makes him unpredictable.
However the real fear Republicans have about Trump has nothing to do with him being president. They fear if he is the (nominee) they will not be able to win in a general election.
He's offended enough folks who would vote against him.
A lot of Republicans believe if he's the nominee Democrats will win.
Both political parties leadership are "pro-establishment". They would rather have someone legislative experience and knowledge of foreign relations. Make Mexico pay for a wall? Immigrant religious ban?
Fear is based around (uncertainty) about the future.