Democratic presidential candidate and former Colorado Gov. John Hickenlooper released a set of proposals Wednesday to curb gun violence, including a call for national gun licenses and raising the legal age to own a firearm. Here are some of the initiatives he's proposing, some of which are based on legislation he signed into law as governor:

Universal background checks : Hickenlooper is calling for national background checks for all gun sales, pointing out that one in five gun purchases do not undergo checks because of existing loopholes. He wants to close loopholes and extend the current three-day waiting period to 10 days in order to close what's known as the "Charleston loophole," which enabled Dylann Roof to purchase guns he used to kill nine parishioners

: Hickenlooper is calling for national background checks for all gun sales, pointing out that one in five gun purchases do not undergo checks because of existing loopholes. He wants to close loopholes and extend the current three-day waiting period to 10 days in order to close what's known as the "Charleston loophole," which enabled Dylann Roof to purchase guns he used to National gun licenses: Gun owners would be required to obtain a national gun license that would also require a background check. The license would need to be renewed online every five years.

Gun owners would be required to obtain a national gun license that would also require a background check. The license would need to be renewed online every five years. Raise minimum age to own a gun to 21: Currently, individuals in the U.S. who are at least 18 years of age may own a gun. Licensed firearms sellers may sell handguns to people who are not under 21 years old. But unlicensed people may sell or transfer handguns to people who are 18 years of age.

Currently, individuals in the U.S. who are at least 18 years of age may own a gun. Licensed firearms sellers may sell handguns to people who are not under 21 years old. But unlicensed people may sell or transfer handguns to people who are 18 years of age. Encourage extreme risk protection orders: Would give grants to states to encourage them to put laws on the books allowing families and law enforcement to remove -- temporarily -- a person's access to guns in order to prevent gun violence, if there are warning signs that the individual poses a danger. Such laws have been passed in Colorado and 14 other states, according to a release from the Hickenlooper campaign.

Would give grants to states to encourage them to put laws on the books allowing families and law enforcement to remove -- temporarily -- a person's access to guns in order to prevent gun violence, if there are warning signs that the individual poses a danger. Such laws have been passed in Colorado and 14 other states, according to a release from the Hickenlooper campaign. Magazine limits and bump stocks : Hickenlooper passed magazine limits in Colorado and is pushing for similar action nationwide. He's also calling for Congress to codify the Justice Department's interpretation of a rule to effectively ban bump stocks, which are used to make legal firearms function in a manner similar to automatic weapons.

: Hickenlooper passed magazine limits in Colorado and is pushing for similar action nationwide. He's also calling for Congress to codify the Justice Department's interpretation of a rule to effectively ban bump stocks, which are used to make legal firearms function in a manner similar to automatic weapons. Assault weapons ban: Calls for renewal of assault weapons ban, which was passed in 1994 and expired in 2004. Some in Congress have tried to renew the ban and failed. Hickenlooper acknowledged in his press release the problems with the earlier ban, noting that gun manufacturers found ways to evade the ban. He believes that the ban introduced by Democrats this year addresses many of the shortcomings of the prior bill.

Boost access to mental health services for children: School-based mental health services and community health centers can help identify and support students "who require more intensive services or...law enforcement intervention," the campaign's press release noted.

Hickenlooper has few friends at the NRA -- he received an "F" rating from the NRA Victory Fund, which states on its website: "Make no mistake about it, Governor Hickenlooper is anti-gun and actively seeks to diminish Second Amendment rights in Colorado and throughout the nation."

Other 2020 Democratic contenders are also weighing in on guns. Last week, California Sen. Kamala Harris announced plans to ban AR-15-style firearm imports. New Jersey Senator Cory Booker recently released a gun plan that also calls for a licensed gun ownership program.

In 2018, over 22,000 people died from firearm suicides in 2016, according to a CDC report.

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Hickenlooper plans to discuss his new gun control proposal with Sandy Hook Elementary School families on Saturday.