GOP Senators who negotiated this weekend's deal on gun legislation rejected several Democrat proposals, including an assault weapons ban for those under 21, as they helped shape an agreement lawmakers believe can become law.

An aide for Sen. John Cornyn, R-Texas, who led talks on the matter, told Fox News that among the Democrat ideas Republicans shut down were an assault weapons ban for 18-to-21-year-olds and a mandatory waiting period for all gun sales. 

Also on the list of Democrat proposals, the Cornyn aide said, were a 21-day waiting period for those under 21 when buying any firearm; a high-capacity magazine ban; universal background checks; safe storage requirements for all firearms in homes; criminal penalties for not storing firearms properly in the home; and a license requirement to purchase an assault weapon.

A separate GOP aide confirmed to Fox News that Democrats supported those proposals during talks. 

Sen. John Cornyn

Sen. John Cornyn, R-Texas, during a Senate Judiciary Committee confirmation hearing on Capitol Hill in Washington, Tuesday, March 22, 2022. (AP Photo/Andrew Harnik) (AP Photo/Andrew Harnik)

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Many of the proposals on the list were rejected outright at the start of talks by Republicans, multiple sources familiar with the talks said. But the idea Democrats pushed hardest was the assault weapons ban for those under 21, those sources confirmed. 

That did not make it into the final framework, however. The only proposal in the deal announced Sunday that deals with 18-to-21-year-olds is an "investigative period to review juvenile and mental health records, including checks with state databases and local law enforcement."

The final framework also incudes provisions on straw purchasing firearms; support for state red flag laws; closing the so-called "boyfriend loophole" that allows court-adjudicated domestic abusers to buy guns if they were not married to their partner; and a clarification on the definition of a firearms dealer. The deal also includes several provisions on mental health and school safety. 

Sen. Chris Murphy, D-Conn., led negotiations on behalf of Democrats. He's repeatedly said he would like to see Congress do more on gun control but that he's willing to take even an incremental deal with Republicans to ensure at least something gets done. Murphy's office did not immediately respond to a request for comment from Fox News Monday. 

Sen. Chris Murphy reacts to the Texas school shooting

Sen. Chris Murphy, D-Conn., spoke from the Senate floor after the school shooting in Uvalde, Texas. (Senate Pool Video)

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"Today, we are announcing a commonsense, bipartisan proposal to protect America’s children, keep our schools safe, and reduce the threat of violence across our country," 10 Senate Republicans and 10 Senate Democrats said in a statement Sunday on the agreement. Cornyn and Murphy were among those senators. 

Because 10 Republicans signed onto the initial framework, there are in theory enough GOP votes to break a filibuster and pass a bill in the 50-50 senate. 

But that number could be tenuous, as lawmakers will still need to write and agree on an actual legislative text – not simply broad principles in a framework. 

Uvalde robb elementary banner

A banner hangs at a memorial outside Robb Elementary School on Friday, June 3. (AP/Eric Gay)

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Senate talks on gun legislation began in the wake of several mass shootings in recent weeks, including one in Uvalde, Texas, which killed 19 children and two adults. There was also an apparently racially motivated mass shooting in a Buffalo supermarket which killed 10 people. 

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Most recently, three people were killed and one injured in a Thursday shooting in Smithsburg, Md. A man opened fire inside a break room at a Columbia Machine factory. 

Cornyn has emphasized that the framework 20 senators agreed to Sunday will not prevent Americans from exercising their Second Amendment rights. In a Sunday tweet, he said, "it will not infringe on the rights on law-abiding gun owners."

Other Republicans, meanwhile, say that they cannot support any legislation that imposes new rules or regulations on owning a firearm and are attacking Cornyn's group for allegedly being squishy on GOP voters' priorities.