With data from iSpot and Inscape

Last night, 12 Democratic presidential candidates took the stage in Ohio for the fourth debate, hosted by CNN and the New York Times: Joe Biden, Elizabeth Warren, Bernie Sanders, Pete Buttigieg, Kamala Harris, Andrew Yang, Cory Booker, Beto O’Rourke, Amy Klobuchar, Julián Castro, Tulsi Gabbard, and Tom Steyer.

First, a look at advertising insights from iSpot.tv, the always-on TV ad measurement and attribution company. In total, there were 81.4 million TV ad impressions over the three-hour debate. 

Five brands accounted for nearly half of all spend over the course of the evening: Freedom from Religion Foundation, NumbersUSA, The Washington Post, Twentieth Century Fox and Warner Bros.

Not counting CNN promos, Warner Bros. was the only brand to run two separate spots: one for Motherless Brooklyn and the other for The Good Liar. Freedom from Religion Foundation, NumbersUSA and The Washington Post each aired one ad twice. Here are the three most-seen ads from last night:

1. NumbersUSA TV Spot, 'E-Verify Works' - 2 airings, 9.37 million impressions

2. Freedom from Religion Foundation TV Spot, 'Church and State' Featuring Ron Reagan - 2 airings, 9.29 million impressions

3. Amazon Prime Video TV Spot, 'Tom Clancy's Jack Ryan: Season One' - 1 airing, 6.03 million impressions

We can also see viewership trends from Inscape, the TV data company with glass-level insights from a panel of more than 11 million smart TVs. Here’s a look at where viewers were tuning in from across U.S. DMAs:

In general, the East and West Coasts had slightly higher tune-in than middle America. Other hot spots included Cedar Rapids-Waterloo-Iowa City-Dubuque, IA; Columbus, OH; Topeka, KS; Flint-Saginaw-Day City, MI; and West Palm Beach-Ft. Pierce, FL DMAs.

Inscape also tracked minute-by-minute viewership for the three-hour debate:

Tune-in rose steadily in the first hour, plateaued a bit, then started a slow decline as the night wore on. There were two main peaks in viewership: First, around 9:25 p.m. ET, when candidates were discussing checking Trump and Russia/Putin, and election security/hacking threats. Then a little later viewership peaked around 9:57 p.m. ET, when Bernie Sanders discussed his health and candidates talked about whether age is an issue.