It was a sea of pale puckered cotton in the Senate on Thursday. 

That’s right, it’s seersucker season again on Capitol Hill.

Donning the Southern staple once a week during the sweltering months has been a Senate tradition since 1996, when Mississippi Republican Trent Lott decided to make it a thing. After a short lapse, Bill Cassidy took over the clothing coordinator duties in 2014 while still in the House, making this his 10th year in the role.  

And this year, the inherently relaxed look of blue-and-white rumpled cotton is going formal. On Wednesday, the Senate adopted a resolution from Cassidy designating Thursday as National Seersucker Day, June as National Seersucker Month and every subsequent Thursday through August as Seersucker Thursday.

When asked why he decided to codify the tradition this year, Cassidy shrugged.  

“I don’t know. We’re just trying to heighten the awareness of it,” he said, pointing to a reporter’s lack of a breathable, striped natural fiber jacket. “People who are ordinarily attuned to what’s going on didn’t realize it [was Seersucker Thursday].”

Cassidy spoke to CQ Roll Call while rushing to the annual seersucker photo op. It was scheduled for 12:30 p.m. outside the Senate chamber, but a Finance Committee hearing on corporate consolidation in the health care sector ran late — Cassidy emerged at 12:40 — so the senator literally fielded questions on the run.

Seersucker moves as well as it breathes, Cassidy said, and he could “totally” go jogging in it. “It’s amazing,” Cassidy said. “It has the weight of pajamas, so of course it’s comfortable.”

More than a dozen of Cassidy’s colleagues, plus a surfeit of Senate staffers, joined him and his longtime partner in fashion crime, California Democrat Dianne Feinstein, in the sartorial celebration this year. They posed for photos just outside the Senate chamber.

“It’s kind of a marking of the time,” said Cassidy. “We work in a Southern city here, but we dress like we were from Minnesota.”

While it sounds like what fortune tellers call a client behind his back, seersucker comes from the “Persian phrase ‘shir-o-shakar,’ meaning ‘milk and sugar,’ alluding to the alternating textures of the fabric” per the resolution’s preamble.

Despite being such a seersucker evangelist, Cassidy still owns only one suit made of it.

Seersucker Thursday may seem puerile to outsiders, but it’s a beloved Senate custom to those who participate. As silly as traditions sometimes are, they remain the sinews of a collective identity. Like norms are to laws, so traditions are to the labels we apply to ourselves — the stuff between the muscle and bone that usually goes unnoticed until something goes wrong. Traditions connect us to the past and, through that, with one another. Not every tradition is worth celebrating, or even upholding — sometimes the past belongs in the dustbin of history — but those that endure tap into a deep human yearning to join together with others in ritual.

And that’s what Seersucker Thursday does. Partisanship runs deep in Congress, right down to the clothes. Spend a little time on Capitol Hill and you can reliably predict a staffer’s affiliation by how they dress: Republican women in heels and pearls, Democratic men eschewing classic cuts. But when everyone decides to dress up like an extra in The Music Man, they elevate their shared identity, the United States Senate, over political party.

So it may be superficial, and it’s definitely silly, but in a nation as polarized as this one, maybe that’s just what the doctor ordered. And so it’s befitting that the resolution declaring Seersucker Thursdays ends on an ecumenical note, by inviting “the people of the United States to don their warm weather finest on National Seersucker Day and every Seersucker Thursday.”