"Broad City" steps back in time to make a big leap forward in an exciting Season 4.

Spring is usually a sign of positive growth. Flowers bloom and lives start afresh as the world awakens from a deep hibernation. Change is in the air.

So it makes sense that “Broad City,” until now, has predominantly taken place during the summer. The baking streets of New York are on fire with perpetual opportunity, and the down-to-clown 20-something best friends Abbi (Abbi Jacobson) and Ilana (Ilana Glazer) have thrived in the summer heat. Nothing changes. It’s been a largely insular universe, and these two are just having a good time while they can.

But in Season 4, the game has changed. That fleeting “live forever” innocence of their early-to-mid-twenties has moved on, and these two surreal dreamers (Abbi an artist, Ilana a free spirit) are facing a stark, bleak reality.

Winter is here — and yet, they persist.

“Broad City” is still the sharp-witted, inventive, and outrageous comedy built on unbreakable pillars of friendship. Abbi and Ilana still smoke, drink, and party whenever they can — which is often — but there’s a notable shift in tone this season. The cold February during which the new episodes were shot evokes a more subdued reality, if not a stark one. Their adventures are more grounded as the mounting challenges of adulthood creep into their lives.

Given all the press devoted to this topic, it would be easy to assume Donald Tr*mp is to blame for the shift. His presence hovers over the season, and there’s even an episode mid-way through Season 4 dedicated to the caustic effects of his election. The series bleeps his name whenever it’s spoken, just like the many curse words Comedy Central’s ever-weakening censors deem too crude for viewers’ ears.

But much like the winter setting is likely more of a coincidence than an artistic choice — both actors are becoming more and more popular, making finding time to shoot Season 4 trickier than ever — Trump, too, isn’t the only reason “Broad City” is growing up. It’s been working toward this for at least one season. The 2016 election, as it did for many others, just made them face reality sooner.

Season 4 opens with an origin story — the ultimate origin story: how Abbi (Abbi Jacobson) and Ilana (Ilana Glazer) first met. Split into two timelines, a la its inspiration and episode title, “Sliding Doors,” the parallel universes are created in 2011 when Abbi and Ilana rush to catch the MTA and either make it on board or miss it and become stranded. You don’t know which timeline represents the true story of how they met until the end.

The episode grapples with inevitability in a fascinating manner. The duo sees their friendship as an unavoidable collision, in that they meet whether they make the train or not, but the results of each timeline aren’t what you expect. One timeline seems too good to be true throughout, as if their blossoming friendship is a little too simpatico. Parallels are drawn to the culture at large — where they see Obama’s election as the next step toward a surefire female president — while the alternate universe forges a more genuine connection when the women acknowledge the shitty things that happen.

But that timeline is more than just commentary on taking progress for granted and the lost innocence of youthful naïveté. Jacobson and Glazer, who co-wrote the episode, hone in on the point that some things are inevitably good and some things are inevitably bad. Time will tell which is which, and they’ve lived long enough to look back, learn, and appreciate what’s in their control.

Aging, along with the maturity, pain, and conflict that come with it, play into that inevitability. Gone are the carefree days of their early twenties. Now they have new, better jobs: Abbi is an office drone, and Ilana has “a dope waiting job and is super rich now.” Both gigs, despite the conflicting descriptions, represent the same incremental step up from their former jobs, as the two ladies start to appreciate a slightly easier life thanks to more money and security.

But there are gray hairs and ex-boyfriends to deal with, too. There’s fresh guilt to go along with their moves up the career ladder and new dynamics to be forged with friends and the world in general.

Abbi and Ilana are growing up, slowly but surely. But it’s not Trump that made them do it. Yes, the Tr*mp-centric episode — directed by Jacobson and titled “Witches” (airing October 25) — feels like a step outside the “Broad City” bubble and into an activist arena, but the series has been building toward this change for a while. Trump’s influence may be all over the three episodes given to critics, in Ilana singing about white guilt while paying for an elaborate manicure or Abbi’s concerns about her physical appearance. But he deserves little, if any, credit for motivating positive change (just like we see with his day job).

Clear earmarks of progress could be seen late in Season 3, such as when Ilana and Lincoln broke up and the free-wheeling sexual dynamo had to face unexpected despair at losing someone she loved; or when Abbi took a trip home to visit her father and we learned more about her past than ever before; or, yes, when Hillary Clinton made a cameo as herself during the 2016 campaign.

The election made a lot of people face a new reality, and “Broad City” is doing just that. It’s engaging in a more serialized storytelling mode, the world itself, and time’s continual march forward. But these creators aren’t letting Trump’s patriarchy dictate their decisions. These scary forces don’t control Season 4; Glazer and Jacobson do, and they’ve never been more powerful.

Winter has arrived, but with it comes growth.

Grade: A-

“Broad City” Season 4 premieres Wednesday, September 13 at 10:30 p.m. on Comedy Central. The first episode is also streaming online now.

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