Donald Trump, center, speaks as Ben Carson, left, and Ted Cruz look on during the CNN Republican presidential debate at the Venetian Hotel & Casino on Tuesday, Dec. 15, 2015, in Las Vegas. (AP Photo/John Locher)

NEW YORK | The Republican presidential debates continue to be a big television draw, with 18 million people tuning in to the confrontation from Las Vegas on Tuesday night.

Donald Trump, center, speaks as Ben Carson, left, and Ted Cruz look on during the CNN Republican presidential debate at the Venetian Hotel & Casino on Tuesday, Dec. 15, 2015, in Las Vegas. (AP Photo/John Locher)
Donald Trump, center, speaks as Ben Carson, left, and Ted Cruz look on during the CNN Republican presidential debate at the Venetian Hotel & Casino on Tuesday, Dec. 15, 2015, in Las Vegas. (AP Photo/John Locher)

The Nielsen company said on Wednesday this made it the third most-watched among the five GOP primary debates that have taken place so far this year.

The first one this summer, seen by 24 million people on Fox News Channel, tops the list. But CNN this week exceeded the viewership for the previous two Republican contests, which both aired on financial news networks.

Tuesday’s Republican debate focused on national security issues and fighting terrorism.