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?
Of the suggestions offered so far I think "smug" is most accurate.
smug (smŭg) adj. smug·ger, smug·gest Exhibiting or feeling great or offensive satisfaction with oneself or with one's situation; self-righteously complacent: a smug look; a smug critic.
Then maybe consider "supercilious" -
su·per·cil·i·ous (so͞o′pər-sĭl′ē-əs) adj. Feeling or showing haughty disdain. See Synonyms at arrogant. [Latin superciliōsus, from supercilium, eyebrow, pride : super-, super- + cilium, lower eyelid; see kel- in Indo-European roots.] su′per·cil′i·ous·ly adv. su′per·cil′i·ous·ness n. Word History: The English word supercilious ultimately derives from the Latin word supercilium, "eyebrow." Supercilium came to mean "the eyebrow as used in frowning and expressing sternness, gravity, or haughtiness." From there it developed the senses "stern looks, severity, haughty demeanor, pride." The derived Latin adjective superciliōsus meant "full of stern or disapproving looks, censorious, haughty, disdainful," as it has since it entered English as supercilious in the 1500s. The super- in the Latin word supercilium means "above," and cilium was the Latin word for "eyelid." In many of the Romance languages, this word developed into the word for "eyelash." This development is probably reflected in the scientific use in English of the word cilium, whose plural is cilia. Cilia are the minute hairlike appendages of cells or unicellular organisms that move in unison in order to bring about the movement of the cell or of the surrounding medium. American Heritage® Dictionary of the English Language, Fifth Edition. Copyright © 2016 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved. supercilious (ˌsuːpəˈsɪlɪəs) adj displaying arrogant pride, scorn, or indifference