Some perspective as to why his Watergate broadcast (which were actually two PRIME TIME
broadcasts on CBS a week-and-a-half before the 1972 Presidential Election), was controversial - Cronkite, the "most trusted man in America" by 1972, decided that he couldn't compete with Washington Post reporters Bob Woodward and Carl Bernstein, so why not have two programs that summarized what the Post reporters had discovered? Up to then, Watergate hadn't reached "Scandal-Status", but Cronkite's broadcasts made Watergate a visual story for the first time. Also, the Washington Post was out on a journalistic branch on their own, and Cronkite's broadcasts provided a much-needed boost. As Ben Bradlee, the chief editor of the Washington Post said, it was a "big kiss" from Walter. It was true that Cronkite was an avowed liberal, especially by 1972 (there was even a grass-roots effort at the Democratic National Convention to convince George McGovern, the presumptive nominee, to have Cronkite run as his Vice-Presidential running mate), but that alone doesn't explain why Nixon absolutely hated Cronkite (and all other members of the media). Cronkite had become one of top names on Nixon's infamous "hit list" long before his extended Watergate broadcast. Among the the reasons was that Cronkite was the only member of the media to be able to conduct not one, but two clandestine television interviews with Daniel Ellsberg, the author of "The Pentagon Papers", an expose on the U.S. Government and Vietnam (think Old-School "Wiki-Leaks"). The FBI couldn't find Ellsberg, Nixon's men couldn't find Ellsberg, but Cronkite did, and the Ellsberg interviews meant that Nixon had a political bulls-eye placed on Cronkite's head. Long before Cronkite's Watergate broadcasts, Nixon and his men tried very hard to isolate and discredit Cronkite as an ultra-liberal with an obvious agenda against the President.
The impact of Cronkite's Watergate extended broadcasts didn't make any difference on that year's election; Nixon won the largest victory in presidential history in terms of states won (49 to 1; McGovern only carried Massachusetts, he didn't even carry his home state of South Dakota). The impact of Cronkite's broadcasts was delayed; it took time for Americans to digest all the information. Also, since Cronkite attached his name to the Post reports, any new development concerning Watergate in the Washington Post had the implied consent and support of Cronkite as well, which lent even more credibility to Woodward & Bernstein's investigative journalism (it also helped that Cronkite kept echoing the Post reports in his nightly CBS newscasts).