As Rashida Tlaib arrived on Capitol Hill to be sworn into the House of Representatives on Thursday, she was wearing a distinctive outfit: a traditional Palestinian thobe, or dress, adorned with the elaborate, hand-stitched embroidery known as tatreez.

[Read live updates from the opening of the 116th Congress.]

Ms. Tlaib, a Democrat from Michigan who is the first Palestinian-American woman to serve in Congress, had posted a photo of the dress on Instagram on Dec. 14, garnering 11,000 likes — but also criticisms, including racist comments.