U.S. Senate candidates Marco Rubio and Patrick Murphy attacked their opponents' ties to their presidential nominees in a debate Monday night at the University of Central Florida.

The debate, at the Fairwinds Alumni Center and hosted by WFTV, ABC News and Politico Florida, was a closed event, with tickets given out only mainly students and professors.

In the past few months, Democrat Murphy and Republican Rubio have exchanged sharp words against each other on the campaign trail, but Monday's debate was largely civil, with each candidate waiting his turn to answer questions.

The Senate candidates shared their stances on topics such as immigration reform as well as the Affordable Care Act, still a hot topic in both Democratic and Republican circles.

"It's not perfect," Murphy said. "There's many things we need to do to improve it, and that's exactly what I've spent my time in Congress trying to do."

"To say that Obamacare has some problems is to say that the Titanic has some problems," Rubio countered. "It has enormous problems."

Murphy attempted to tie Rubio to GOP presidential candidate Donald Trump, who beat him badly in Florida's presidential primary earlier this year and in recent weeks has been forced to defend himself after vulgar comments about women he made more than a decade ago resurfaced.

"I've condemned him when he's said things that are aggressive, outrageous, vulgar and inappropriate, and I will continue to do so," Rubio said.

"This isn't just a binary choice, and there are people who have the courage to stand up and do what’s best," Murphy said.

For many at UCF, the debate — just 21 days before the general election — offered an opportunity not just to showcase the school on a televised stage, but also to potentially make a mark on the election and undecided voters.

Before the debate, UCF students on both sides of the political fence gathered on the quad, chanting and carrying signs.

"It's getting a little confrontational, so I can understand," said Alexander Molennear, a UCF sophomore studying political science who supports Murphy.

"(Rubio) hasn't done his job correctly, so I’m here for the correct candidate," he said.

Donning a sailor cap to demonstrate how he thinks Murphy is privileged, Luke Strominger couldn't disagree more.

"I don't think we need Democrats anymore," Strominger said. "We need our state to go red."

"It's quite the experience. As a student, I didn't think that I’d have this opportunity so have such an elite presidential, or prior presidential candidate and now Senatorial debate happening here in Florida," UCF communications student Lauren Cruz said, a volunteer who helped coordinate the event.

Faculty at UCF also touted the school's opportunity to influence politics.

"It speaks I think to what the university has become and why it continues to grow and why it's seen, quite candidly, as the type of place you'd want to have this event," said Tim Brown, an associate professor of Radio and Television. "I think what it shows is that Orlando is a key to Florida, which is a key to the national election."

The Senate seat is a key to Republicans holding a majority in the Senate and is critical for Rubio to win if he has further presidential aspirations. For his part, Murphy was backed by the Democratic establishment ahead of his primary victory over U.S. Rep. Alan Grayson.

"It's an honor for UCF to hold the debates," Molennear said.

Rubio and Murphy will debate again at Broward College in Davie next week.

Several armed men trespassed at event

As the debate started, four men who tried to enter the debate were trespassed from campus, according to UCF Police spokeswoman Courtney Gilmartin.

Gilmartin said a third-party candidate who was not invited to the event tried to enter the Alumni Center without a ticket. The candidate had security with him who were armed, which is in violation of a Florida law preventing guns on college campuses unless they're in a locked vehicle.

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