Donald Trump's questions about Ted Cruz's eligibility to be president, which have dominated the news cycle all week, also dominated the first Republican debate of 2016.
The top social moment of the debate on Facebook came when the Texas senator said, "I have spent my entire life defending the constitution before the U.S. Supreme Court and I'll tell you I'm not going to be taking legal advice from Donald Trump."
He was referring to the businessman's advice that Cruz obtain a legal judgment that he is a natural-born citizen and thus eligible to run for president (Cruz was born in Canada to an American mother and Cuban father, and has insisted that makes him a natural-born citizen who is eligible for the presidency).
Among the problems, Trump suggested, was that if he chose Cruz as his vice president - or if Cruz won outright - Democrats would challenge his eligibility.
"You should go out, get a declaratory judgment," he advised. "Let the courts decide."
"There is a big question mark on your head. And you can't do that to the party. You really can't. You can't do that to the party he added.
Unsurprisingly, Trump and Cruz were the top two candidates discussed on Facebook during the debate. Next was Sen. Marco Rubio -- who also went on the attack against Cruz at the end of the debate -- followed by neurosurgeon Ben Carson and New Jersey Gov. Chris Christie.
There was no in-depth discussion of Iran or the nuclear deal with that that country, but it was still the top issues discussed on Facebook during the debate. Facebook users were also talking about immigration, the Islamic State of Iraq and Syria (ISIS), the economy, and guns.
The most engaged states were New Hampshire, which has its primary election in February; its neighbor, Vermont; South Carolina, where the debate was held, Virginia; and New Jersey.