Democratic candidates for president square off tonight in their first debate. A University of Missouri professor says if Hillary Clinton wants to remain the frontrunner, she has some work to do.

University of Missouri Professor of Communication Mitchell McKinney (courtesy; MU)

University of Missouri Professor of Communication Mitchell McKinney (courtesy; MU)

Bernie Sanders has a great deal of support and many are watching whether Joe Biden will enter the race. University of Missouri communications professor Mitchell McKinney says Clinton cannot shrug off attacks by other candidates, as he says she did in debates in past campaign cycles.

“She often would take what I called a sort of, ‘above the fray,’ stance. When she was attacked she would try to brush it off with laughter frequently. I don’t think she can take that same approach and stance now. She’s got to secure the nomination if it’s going to be hers,” said McKinney.

McKinney says in recent days Clinton has been setting up possible debate topics, such as a focus on gun control, “as a way, I think, to smartly contrast her positions in that area as opposed to Bernie Sanders, whose previous votes and his approach to that issue may not be so appealing to some Democrats.”

Other issues McKinney says Clinton is trying to draw attention to is education reform and funding, and a contrast to Sanders’ proposal of a free college education for all.

He says if Clinton doesn’t turn in strong debate performances, “I think it would only fuel the fire of, ‘We need to recruit Joe Biden to the race.'”

Besides Clinton and Sanders, tonight’s debate features candidates Martin O’Malley, Jim Webb, and Lincoln Chafee. Biden could still join them.

The CNN debate is at 7:30 cst.