There were fireworks onstage during the second-to-last Republican presidential debate before the Iowa caucuses on February 1, as Donald Trump and Ted Cruz, who are running neck and neck in Iowa, traded attacks. NY1's Grace Rauh filed the following report.

Texas Sen. Ted Cruz has been polling well in Iowa, and Republican front-runner Donald Trump is stepping up his attacks, including one that has been widely discredited. Trump is questioning whether Cruz, who was born in Canada to an American mother and a Cuban father, is constitutionally eligible to be president.

"There's a big question mark on your head, and you can't do that to the party," Trump said.

"The chances of any litigation on this proceeding and succeeding are zero," Cruz responded.

Cruz did say he'd consider naming Trump as his vice president. Cruz said if Trump turns out to be right, he'd become president.

Cruz, meanwhile, has been fighting back, accusing Trump of having quote "New York values."

"Not a lot of conservatives come out of Manhattan. I'm just saying," Cruz said.

Trump tried to turn the tables by invoking the September 11th terrorist attacks.

"When the World Trade Center came down, I saw something that no place on Earth could have handled more beautifully, more humanely than New York," Trump said.

Trump doubled down on his proposal to ban Muslim visitors and immigrants from entering the U.S., while others objected.

"All Muslims? Seriously? What kind of message does that send to the rest of the world that the United States is a serious player in creating peace and security?" said Republican presidential candidate Jeb Bush.

Florida Sen. Marco Rubio, who supported a bipartisan immigration reform bill in 2013, defended his movement on the issue.

The entire system of legal immigration must now be re-examined for security, first and foremost, with an eye on ISIS," Rubio said. "Because they are recruiting people to enter this country as engineers, as doctors, posing as refugees. We know this as a fact.

New Jersey Governor Chris Christie, Ohio Governor John Kasich and Dr. Ben Carson also shared the stage.

This is the second-to-last debate before the Iowa caucuses on February 1.