John de Lancie plays a presidential contender named Kurt Seaman in “Vicuña & the American Epilogue.” (C. Stanley Photography)

In Jon Robin Baitz’s scaldingly funny “Vicuña & the American Epilogue,” the wannabe emperor has new clothes. But like everything else about him, they’re threaded with ersatz values and designed to fall apart.

The penetrating comedy in Mosaic Theater Company’s space at the Atlas Performing Arts Center, directed with aplomb by Robert Egan and filled with fine performances — beginning with John de Lancie as what you might call the Vulgarian Candidate — is the first top-drawer political play of the Trump era. It’s satisfying because even though it’s satire, it takes the presidential contender, here named Kurt Seaman, deadly seriously. And it portrays those close to him not as cardboard-cutout toadies but as desperate comic characters spinning around the drain of an enveloping cataclysm.

“I have to convince decent, ­hard-working people that what America needs is the best version of my dad,” is how the candidate’s campaign-manager daughter, played to the pristinely manicured hilt by Laura C. Harris, describes her Faustian bargain and soul-withering dilemma. “My heart hurts, and my friends find me slightly soiled.”

The notion of a morally convulsed Ivanka — here called Srilanka — may be wishful thinking on the part of Baitz, the author of, among other plays, “Other Desert Cities,” and now writing the second season of the FX cable channel’s “Feud.” The device, though, is only one of many pleasingly inspired flights of writerly fancy sprinkled over an evening of perspicacious insights and devastating verbal takedowns.

“Vicuña” was staged once before, by the Center Theatre Group in Los Angeles, right before the 2016 elections, and it proved eerily prescient. Baitz has added for Mosaic “The American Epilogue,” a short, and potent, capstone based on a physical assault that the playwright alleged occurred against him in Washington at the time of Donald Trump’s inauguration; the trial of the accused assailant is scheduled to begin here in December. That Mosaic nabbed it for its East Coast premiere is an impressive coup for this probing and increasingly important company. It’s impossible to believe that the play won’t be snatched up by other ambitious groups along the Eastern Seaboard and beyond.

Set in the atelier of a gentleman’s bespoke tailor shop in Manhattan, rendered with luxe, eye-pleasing refinement by designer Debra Booth, “Vicuña” recounts the measuring and production of a $150,000 suit for businessman-candidate Seaman to wear for his final televised debate with his female opponent, who here remains cheekily nameless. The material for the garment is the finest money can buy, and the tailor, one Anselm Kassar (the wonderful Brian George), has been a clothier to presidents past. He’s also an Iranian Jewish immigrant whose apprentice, Amir Masoud (Haaz Sleiman, in a seductively virile turn), is from an Iranian Muslim family. When Amir meets Srilanka — engaged to a Jewish real estate scion in a marriage of corporate convenience — the embers of a forbidden alliance are stoked.

Baitz is playing here buoyantly with the poetic implications of a power suit and what it means for this cultured tailor to lend his talents to selling a dangerous man whose reputation has been built on a myth of professional prowess — a candidacy, in essence, made of whole cloth. To de Lancie’s credit, Seaman doesn’t come across as a caricature; neither vacuous nor out of touch with reality, this candidate has a maturer command on his belief system than one might glean from the real public figure on whom he is clearly modeled. But he’s also recognizably ruled by out-of-control appetites and grievances and contempt for ­people like the fearless, Harvard-educated Amir. That de Lancie makes him palatable is the mark of a terrific pretender.

Egan and Baitz, with the help of the chic and witty work of costume designer Brandee Mathies, devise an ingenious sartorial comeuppance for Seaman (whose self-mockingly clumsy new slogan is “Seaman loves women and women love Seaman.”) And in the person of the divinely officious Kimberly Schraf, portraying a U.S. senator and Republican National Committee chairwoman dispatched to do anything to get Seaman off the ticket, “Vicuña” offers a most delicious rant into the face of Seaman, the sort of speech audience members might want to rehearse themselves and, in one distressing moment of CNN or MSNBC viewing, recite at full volume at the television set.

The newly written “American Epilogue” Baitz has appended is of a wholly divergent tone from what has come before on this invigorating evening. It’s mournful, even solemn, but not righteous or resigned. If anything, it’s a consoling finale, suiting you up for whatever struggle you may believe lies ahead.

Vicuña & the American Epilogue, by Jon Robin Baitz. Directed by Robert Egan. Sets, Debra Booth; costumes, Brandee Mathies; lighting, Alberto Segarra; sound, Karl Lundeberg; properties, Michelle Elwyn; stage manager, C. Renee Alexander. About 2 hours and 10 minutes. Tickets $20-$65. Through Dec. 3 at Atlas Performing Arts Center, 1333 H St. NE. 202-399-7993, Ext. 2. mosaictheater.org.