Debates by the numbers

In advance of tonight's Democratic debate, which airs at 9 on MSNBC, Nielsen has compiled national ratings for the previous presidential showdowns. (It's also a healthy reminder of just how much the candidates have sparred during this long primary season.)

The numbers vary broadly, from 960,000 viewers for MSNBC's Republican forum in Chicago on Aug. 7 to 3.14 million for Fox News Channel's Republican forum in New Hampshire on Sept. 5. Here's a quick rundown:

April 16 Democratic debate (MSNBC): 2.26 million viewers
May 3 Republican debate (MSNBC): 1.76 million viewers
May 15 Republican debate (Fox News): 2.55 million viewers
June 3 Democratic debate (CNN): 2.78 million viewers
June 5 Republican debate (CNN): 2.06 million viewers
July 23 "YouTube" Democratic debate (CNN): 2.62 million viewers
Aug. 5 Republican debate (ABC): 2.19 million viewers
Aug. 7 Democratic debate (MSNBC): 960,000 viewers
Aug. 19 Democratic debate (ABC): 2.87 million viewers
Sept. 5 Republican debate (Fox News): 3.14 million viewers
Sept. 9 Democratic debate (Univision): 2.2 million viewers
Sept. 26 Democratic debate (MSNBC): 1.47 million viewers
Oct. 9 Republican debate (CNBC): 1.02 million viewers
Oct. 21 Republican debate (Fox News): 2.37 million viewers