Surprisingly, the question seems to surprise Jake Tapper: Why would the best-known reporter at ABC News jump ship to join CNN, the floundering cable network that a lot of people in the industry — a lot of people — regard as the TV news version of the Titanic?

“That’s not how I see it,” he replies, his tone one of consternation blended with bewilderment. “CNN is a vital place. More people watched the election results on CNN than any other channel. More people watched the inauguration on CNN than any other channel. … MSNBC and Fox News are great at what they do, but that’s very different from what we do. So I just reject your characterization.”

Not my characterization, the reporter corrects him; I said, “a lot of people see it that way,” not necessarily me. Tapper snorts. “I’ve used that construction myself, my friend,” he says affably. “I know exactly what you meant.”

So there you have it: Jake Tapper takes no more guff when he’s being asked the questions than he does when he’s asking them. Famously combative in the pursuit of a story, Tapper now parachutes into a battle that his side has been losing badly. His show The Lead with Jake Tapper debuts Monday in a CNN lineup that in recent years hasn’t been much more than target practice for Fox News and MSNBC.

A decade-long downhill slide in the ratings has left CNN in a weak fourth place among cable news nets, trailing even corporate cousin HLN. CNN’s average daily audience is less than a third of what’s drawn by leader Fox News. The numbers are even worse in prime time, where Fox News has nearly four times the audience of CNN. In the 4 p.m. slot that Tapper is taking over, CNN has been drawing an average of 461,000 viewers during the past two weeks; Fox News, 1.29 million.

Seeking to put a tourniquet on its hemorrhage of viewers, CNN hired former NBC boss and Today Show auteur Jeff Zucker as president. Tapper was his first big hire, though talks between the reporter and CNN were already under way when Zucker took over.

“I had to talk to a lot of people and places, but fundamentally it was down to staying at ABC or moving to CNN,” Tapper says. “I was very serious about CNN, but I hadn’t make any decision. Jeff came along at the right time. I think he’s going to offer the kind of leadership this place needs.”

Zucker, Tapper says, shares his conviction that “CNN is already the place people go when there’s a big breaking story, and now it needs to be better at attracting people where there isn’t a big breaking story. We need to present the news in an aggressive but nonpartisan way … .

“There’s a huge audience for news out there. People get news from the Internet, from their cellphones, from Twitter, from the radio in their cars. We just have to convince them that we are a place to go for news because we have a good product, and the way to do that is to produce a great product. I don’t think there’s a finite number of cable-news viewers and we’re all competing for the same audience. There’s a much bigger audience we can draw from.”

Tapper was twice passed over for the job hosting ABC’s Sunday-morning talk show This Week, at least partly because he told his bosses that if he became the anchor he would broaden its news focus outside Washington. But he says the failure to get that post is not exactly the reason he took the job at CNN, at least not in any snitty to-hell-with-you-ABC way.