Michael Lombardo may not have been pushed overboard at HBO. But as he disembarks, the ship is taking on water.

Lombardo, whom Variety reported Friday will step down as HBO programming president, is a 33-year veteran of the premium cable channel. Promoted to his current role in 2007, he oversaw the network’s resurgence following the end of “The Sopranos” and the departure of former CEO Chris Albrecht. Under current CEO Richard Plepler, he developed a fleet of hits, Emmy winners and critical darlings that includes “True Blood,” “Eastbound & Down,” “Boardwalk Empire,” “The Newsroom,” “Girls,” “Veep,” “True Detective” (well, the first season) and “Silicon Valley.” Lombardo’s most important legacy is “Game of Thrones,” the series that through its record-breaking Emmy hauls and outsize ratings has defined HBO in the post-“Sopranos” era.

But with “Game of Thrones” set to end after two more seasons, HBO now faces a transitional period. The shows that have been its calling card under Lombardo are all graying — and no obvious replacements are on the horizon.

HBO’s development pipeline has, in the last year, become clogged with dead and hobbled projects. High-profile miniseries “Lewis & Clark,” from exec producers Tom Hanks, Brad Pitt and Edward Norton, halted production last August, then went into redevelopment in February with writer Michelle Ashford. The Jonathan Nolan-produced “Westworld” stopped production in January and didn’t resume for three months. HBO pulled the plug on “Utopia,” a drama set to reunite “Gone Girl” writer Gillian Flynn and director David Lynch last August, more than a year and a half after greenlighting the series.

The shows that have actually made it to HBO’s schedule have been no less problematic. Comedies such as “Togetherness,” “The Brink,” “Family Tree” and “Hello Ladies” failed to connect with viewers and were canceled. The network’s drama troubles have been even more serious. “Vinyl,” HBO’s biggest drama swing in years, with a pedigree that includes executive producers Mick Jagger and Martin Scorsese, received mixed reviews and poor ratings. HBO renewed the series for a second season after only one episode aired, but last month the network tossed showrunner Terrence Winter, replacing him with Scott Z. Burns.

Then there’s “True Detective.” The anthology series was a breakout hit for the network when it premiered in 2014 with a season-one arc starring Matthew McConaughey and Woody Harrelson. But the second season, retaining writer Nic Pizzolatto but with a new cast and director, was widely panned. Ratings for the season-two finale were down 22% in total viewers from the end of season one. HBO subsequently extended Pizzolatto’s development deal but has been non-committal about a third outing.

Amid these troubles, HBO in January showed the door to top drama executive Michael Ellenberg and promoted his comedy counterpart Casey Bloys to president of series, specials and late-night. The move came fewer than two weeks after “Westworld” halted production.

With Lombardo now exiting, whomever takes charge at HBO will need to start moving quality product through the pipeline quickly. It is still unknown when “Lewis & Clark” and “Westworld” will finally grace screens. Since Bloys’ ascension, the network has ordered two new dramas — James Franco’s “The Deuce” and Flynn and Marti Noxon’s “Sharp Objects.” The former is about the New York porn industry in the late ’70s and early ’80s; the latter about a reporter investigating the murder of a preteen girl.

Neither appears to have the broad-appeal potential of “Game of Thrones.” The show’s sixth season premiered last month to 8 million total viewers — its most watched episode ever. “Game of Thrones” is now the second most-watched show on cable behind AMC’s “The Walking Dead,” despite HBO being in only a fraction of the homes that AMC and other ad-supported networks are in.

Speaking to Variety earlier this year, Lombardo downplayed the importance of “Game of Thrones.”

“We do believe that every show we put on needs to aspire to its own greatness,” he said. “It’s nice to have a show [like ‘Game of Thrones’] that hits this kind of zeitgeist of popular culture. At the same time, it’s really just one piece of a bigger tapestry for us, and I never lose sight of that.”

That tapestry, however, has been fraying. One year after launching standalone streaming service HBO Now, the network faces more competition than ever in the original programming realm. An April survey by Morgan Stanley found that more consumers believe Netflix has the best original content of any premium TV or Internet-video subscription service — the first time in the six-year history of the survey that HBO did not come out on top.

Speaking on a conference call in February, Jeffrey Bewkes, CEO of HBO corporate parent Time Warner, bragged that the network had added 2.7 million customers in 2015. And HBO has landed a string of programming wins in nonfiction with the success of John Oliver’s “Last Week Tonight,” Andrew Jarecki’s “The Jinx,” and Beyonce’s “Lemonade,” as well as new deals for upcoming projects with Vice, Bill Simmons and Jon Stewart.

But HBO’s continued growth is largely dependent on maintaining its aura of original-programming superiority — a tough challenge in an ever more competitive marketplace. To do that, it must develop new, better shows, specifically on the drama side. And it must stop stumbling in the process.