The first Clinton-Trump Debate was seen by a record 84m TV viewers in the US

"The first televised skirmish between Hillary Clinton and Donald Trump broke the all-time TV audience record for a presidential debate, averaging 84 million viewers across a dozen ad-supported broadcast and cable networks and PBS.
Monday night's showdown between the former Secretary of State, U.S. Senator and First Lady and her opponent, the real estate mogul, steak wrangler and reality TV star, surpassed the 80.6 million viewers who tuned in for the lone debate between President Jimmy Carter and former California Gov. Ronald Reagan in 1980. That event aired on the three extant broadcast networks: ABC, CBS and NBC.
The total Nielsen turnout does not include viewers who streamed the debate online or watched from a bar, restaurant, hotel or other out-of-home venue. Also not included in the final debate tally was C-Span, which is not officially measured by Nielsen.
NBC boasted the largest debate audience, drawing 18.2 million viewers, or 22% of the overall viewership for the 99-minute event. ABC scared up the second-largest crowd, averaging 13.5 million viewers, while CBS took third with 12.1 million. Fox News Channel claimed the biggest debate crowd among the cable news outlets, drawing 11.4 million viewers, while its rival CNN averaged 9.94 million. MSNBC finished near the back of the pack with an average delivery of 4.91 million viewers.
NBC also won the night among the core news demographic, averaging 8.3 million adults 25 to 54 to CBS's 4.8 million and ABC's 4.75 million. CNN's coverage drew 4.51 million members of the demo, topping the much older-skewing Fox News Channel's 3.55 million and eclipsing MSNBC's average delivery of 1.59 million demographically apposite viewers.
As has been the case with every presidential debate since the first televised joust (Nixon-Kennedy, Sept. 26, 1960), Monday night's proceedings were uninterrupted by commercial messages. Pre- and post-debate ads on the Big Three broadcast networks went for as much as $250,000 per 30-second spot."
Source:  AdAge, 27th September 2016