Walter Cronkite, anchorman for CBS, was, perhaps, the most instrumental in destroying Nixon because he took the story of the Watergate break-in from the back pages of the Washington Post to the front.
Outside of the Washington Post, few news outlets gave the story that much play. After Cronkite pieced the elements together, they could ignore it no longer.
After Cronkite's journalistic efforts, other news organizations picked up the story, and the rest is history.
Washington Post reporters Bob Wooddall and Carl Berstein began deeper investigations and made contact with an informant, dubbed "Deep Throat" by Howard Simons, managing editor of the Post at the time. (Shortly before his death, this informant revealed himself as a former Associate Director for the FBI, Mark Felt.) The results of their investigations were later published in a book entitled All the President's Men. (1974)
When the Watergate hearings began, the major networks broadcast them for hours and hours every day, to the exclusion of other programs. People had no choice but to watch these hearings if they wanted to watch TV because in those days, there were only three major networks.