Democrats are getting their long-awaited first debate of the presidential primary season Tuesday night, with five candidates set to take the stage: Lincoln Chafee, Hillary Clinton, Martin O'Malley, Bernie Sanders and Jim Webb.

Here's four tough questions head debate moderator Anderson Cooper should ask the candidates:

Gun Control

"In the wake of the tragedy at Umpqua Community College, many of you have called for more gun control. Oregon's restrictions on gun sales already include mental health and criminal background checks, yet this tragedy occurred anyway. With that in mind, what is your plan for passing legislation that would effectively reduce mass shootings in the United States?"

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