The fifth Republican presidential debate scheduled for Dec. 15 in Las Vegas is shaping up as a mega-battle between the competing candidates Donald Trump and Ted Cruz.

The front-running Trump launched his first public attacks against the surging Texas Senator on Friday, simultaneously questioning his appeal to evangelical voters and his commitment to ethanol subsidies.

Since launching his campaign roughly five months ago, Cruz has largely refrained from calling out Trump, but all that politeness may come to a screeching halt when the two men next come face-to-face at Tuesday night's debate.

Part of Trump's motivation for now turning his attention to Cruz could stem from his rising poll numbers in the critical early-voting state of Iowa. The loquacious Texas senator also recently openly wonder if the bombastic real estate mogul has the political chops to oversee the nation in a time of such terrorism.

"I do like Ted Cruz, but not a lot of evangelicals come out of Cuba," Trump recently told a crowd of supporters at a town hall gathering in Des Moines. "Not a lot come out."

Trump's personal attack on Cruz mirrors the approach he recently took to political neophyte Ben Carson when the retired neurosurgeon jumped to a surprising lead in several national polls. Carson is a Seventh Day Adventist, while Trump, who identifies as Presbyterian, has also implied that he is more of a mainstream Christian.

Prior to their now increasingly public spat, both Trump and Cruz had made certain to lavish much praise on one another, with both men indicating that he could see how the other could effectively serve in his administration.

"We would certainly have things in mind for Ted," Trump once echoed.

The event will be moderated by Wolf Blitzer on CNN and will air at 8:30 p.m. (ET) from the Venetian in Nevada. You can watch the livestream here.