Let’s talk about the “bra strap” dress that Ivanka Trump wore to her father’s first address to a joint session of Congress last night, a pink, one-shouldered number reportedly by French designer Roland Mouret. Its boudoir-ish black strap was meant to look like a bra strap, of course, and it heightened the sex appeal of Ivanka’s bare-shoulder look, which was perhaps better suited for date night than a speech in Congress. It was an unconventional choice for such a serious occasion, which made it all the more un-Ivanka. Since moving to Washington, she’s glammed it up for black-tie affairs like...