Donald Trump and Ted Cruz shake hands at the start of the Republican candidates’ debate sponsored by CNN in March. (Joe Skipper/Reuters)

Looking for someone specific to hold responsible for the improbable rise of Donald Trump?

Although there are many options, you could do worse than to take a hard look at Jeff Zucker, president of CNN Worldwide.

It was Zucker, after all, who as the new head of NBC Entertainment gave Trump his start in reality TV with “The Apprentice” and then milked the real estate developer’s uncanny knack for success for all it was worth in ratings and profits.

“The show was built as a virtually nonstop advertisement for the Trump empire and lifestyle,” according to the book “Trump Revealed,” by Washington Post journalists Marc Fisher and Michael Kranish.

And it succeeded wildly — boosting the network’s ratings, as well as Zucker’s meteoric career. In turn, under Zucker, the show gave rise to “Celebrity Apprentice,” another Trump extravaganza. And, in turn, Zucker became the head of NBC overall.

While hosting "Celebrity Apprentice" on NBC, Donald Trump promised to give to charities over 20 times. It turns out that the money given away wasn't actually from him. (Daron Taylor,David Fahrenthold/The Washington Post)

The executive rode the Trump steed hard. When the reality-TV star was preparing to marry Melania Knauss in 2005, Zucker wanted to broadcast the wedding live. (Trump, uncharacteristically, declined.)

But make no mistake: There would be no Trump-the-politician without Trump-the-TV-star. One begot the other.

Ten years later, it was Zucker, now the head of CNN, who gave Trump astonishing amounts of free exposure in the Republican presidential primary on the cable network, continually blasting out his speeches and rallies — often unfiltered and without critical fact-checking.

“It’s a not-unfair knock on CNN to say that they went all in on Trump and helped him enormously,” Ken Lerer, co-founder of the Huffington Post and BuzzFeed, said in a recent onstage interview at City University of New York’s journalism school. “I think it was a strategy, a programming strategy.”

Of course, CNN was hardly alone. Fox News, too, has been a megaphone for Trump for many months. And nearly every news outlet has played a part — from newspaper front pages to NPR to the network nightly news.

Ratings. Clicks. Audience. Say what you will about Trump as a human being or a potential leader of the free world, he has an ineffable ability to get attention. He has called himself a “ratings machine,” and in the world of TV, ratings equal profit.

“It may not be good for America, but it’s damn good for CBS,” Leslie Moonves, chairman of CBS, said of the Trump phenomenon in March, according to the Hollywood Reporter.

Jeff Zucker, then president and CEO of NBC Universal, arrives at the Simon Wiesenthal Center in Los Angeles in 2010. (Kevin C. Cox/Reuters)

“The money’s rolling in, and this is fun. It’s a terrible thing to say. But bring it on, Donald. Keep going.”

Moonves’s ebullience makes it clear that ratings madness infects all of commercial TV, although, of course, particularly the cable-news channels.

None rolled out the welcome mat more eagerly than CNN, which has billed itself as the “most trusted name in news.” And unlike Fox, which is blatantly conservative, CNN pitches itself as nonpartisan. It’s supposed to be the down-the-middle alternative to Fox and, on the left, MSNBC.

And it’s been CNN, too, that has employed former Trump campaign manager Corey Lewandowski as an analyst, where he is bound by a nondisclosure agreement to say nothing negative about Trump, and where he has — until last week — continued to be paid severance by the campaign even while promoting the candidate on the air.

To be sure, CNN also boasts many fine journalists, and in recent weeks, the network has become much tougher on Trump. Apparently, the candidate noticed. Not only has he retreated to Fox News, but his September tweets also show a certain lack of gratitude for past help, calling CNN “unwatchable” and Zucker himself a failure.

Undeniably, the political coverage is working for all the cable news networks. Ratings out last week show sky-high viewership for all three — and that’s manna from heaven in an industry whose numbers were tanking in 2014 and where average viewers are over 60 — while millennials cut the cord and stay glued to their phones.

I asked Zucker, both directly and through his representative, to comment for this column but was told he wasn’t available to talk about it. In the past, he’s brushed off the idea that CNN has been anything but responsible in its coverage decisions.

Can you blame a TV executive such as Zucker for doing his job — striving for the highest possible ratings and profits?

Maybe not at NBC, where as the head of the entertainment division, Zucker bore no responsibility to the public interest when he made Trump a reality-show star.

But when it comes to CNN’s news coverage — its journalism — that’s a different matter. Decisions about covering a presidential campaign should consider what’s best for citizens as well as what’s best for Time Warner’s shareholders.

Some would say that CNN merely held up the mirror to Trump, and voters freely chose him over his Republican competitors. And now, voters may freely choose him over Hillary Clinton, who has made the coverage problem worse by being the anti-Trump — failing to connect emotionally with voters and even at the basic political task of making news. Partly by being so guarded, she’s ceded the near-monopoly on news to her more charismatic rival.

But it is, after all, the responsibility of the press to hold candidates accountable, not to provide publicity.

Twice, Zucker made Trump a winner. And twice, Trump made Zucker a winner.

But what about the rest of us?

For more by Margaret Sullivan visit wapo.st/sullivan