COUNCIL BLUFFS, Iowa — The aspiring Republican presidential candidates have logged countless hours in the living rooms of voters, pitching their platforms and firing jabs at President Obama.

Yet there is one difference this election season. The contenders, even here in the early-voting states, are far more likely to make their visits on television than to ever drop by in person.

In what is shaping up as a profound change in American politics, the living room stops and the cafe visits where candidates offer handshakes and make appeals for support are creeping toward extinction. The onetime fixtures of the campaign trail are giving way to the Fox News studio and televised debates.

It has been five decades since television began to transform presidential races, but never before have the effects of cable television been so apparent in the early stages of a campaign.

The latest sign can be found in the resurgence of Newt Gingrich, who is now trying, with little more than a month before the voting starts, to build an on-the-ground organization in states that can keep up with his on-the-air popularity. He has spent less time at traditional campaign events and more time on television than almost any of his rivals.

“Everything has changed,” said Gov. Sam Brownback of Kansas, who traveled across Iowa as an unsuccessful Republican presidential candidate four years ago. “It’s like a town hall every day on Fox News. You hear people talking back to you what you saw yesterday on Fox. I like Fox, and I’m glad we have an outlet, but it is having a major, major effect on what happens.”

The Fox News effect is amplified by other factors. Cable networks are staging more debates than ever, obliging candidates to build their fall schedules around preparing for and traveling to the slickly produced televised clashes, and putting a premium on skills different from those of retail campaigning