It wasn't (just) 'arrogant', it included a complete disregard for facts, rules, procedures, and other members.
It's the same attitude that many have throughout government (and media) with regard to investigating election fraud and/or the China Flu.
And it's more than 'condescending', it's a word that means 'stare straight ahead and damn the facts - I've got an agenda'. It's a word that signifies 'I am in power, and I am ignoring you'.
What is the proper word?
They were pernicious toward the sitting President.
Their remarks toward the president were callous and disrespectful.
They were both impervious to the truth.
They showed biased disregard for rules and procedures.
They conspired to smear the President.
Their unctuous faux trial was a complete farce.