The 2016 front-runners for each party are going at it publicly, with what could be a preview of the presidential election next year.

Donald Trump greets guests at a campaign rally on December 21, 2015 in Grand Rapids, Michigan. (Photo by Scott Olson/Getty Images)

Donald Trump is calling Hillary Clinton a liar, following her claim that he has become recruiting fodder for Islamic extremists.

Trump took to Twitter, demanding an apology from Clinton.

At a rally last night, he called Clinton "Crooked" and "Not a President".

When asked if she would apologize, Clinton said "Hell No."

He fired back at Clinton by bringing up her election track record, citing specifically the 2008 Democratic nomination she was favored to win but lost to Barack Obama.

Trump said he is the last person Clinton wants to face in a general election.