Senate gun negotiations have reached a critical stage, and hiccups are starting to show.

Senator John Cornyn (R., Texas) is one of the most important signatories to the framework. He has long been the GOP’s go-to man on gun policy. He was key to getting the framework together. He’s also now the most publicly pessimistic about the deal making it across the finish line.

Cornyn had initially said he hoped to get the text of the bill done by the end of this week, which could still happen, but he’s become more pessimistic as the week has gone along.

“I’m frustrated,” Cornyn told CBS News reporter Alan He on Thursday. “I’m not as optimistic right now. But we’re continuing to work.”

So, what are the potential sticking points, and why are they so hard to work out? We only have the barebones framework, comments from Senators, and reporting about the negotiations to go off of right now since the bill’s text isn’t out yet. But what we have gives us some insight into the issues at play.

Red Flag Grant Program

While the Senate framework proposal appears to try and avoid direct controversy over the temporary gun confiscation orders by making its proposal a grant program rather than a national red flag law, a sticking point remains. Republicans want to expand this provision to fund more than just red flag laws. Cornyn said states that don’t pass red flag laws should have access to the same funding for other programs aimed at preventing mass shootings.

“One of the issues has to do is whether the funds that we will vote for will be available to states that don’t have red flag laws, but do have crisis intervention programs and things like mental health courts, veterans courts, assisted outpatient treatment programs,” he told CNN’s Manu Raju on Wednesday. “I just don’t think anything that funds 19 states for their programs but ignores other states that have chosen not to have a red flag law but rather have other ways to address the same problem is going to fly.”

This could create an impasse for a couple of reasons. First, the framework already includes a provision to expand a mental health crisis response program to all 50 states. Second, it further diminishes the potential incentive for states to pass red flag laws. According to Cornyn, everyone is on the same page about those things.

“We’re not incentivizing states that don’t have red flag laws to pass them,” Cornyn told Dana Loesch on Wednesday. “That would be inappropriate.”

But it’s an open question if the program doesn’t do much to increase the adoption of red flag laws among the 31 states who don’t already have one, will Democrats view it as consequential enough to go along with the changes?

Expanding Definition of Domestic Violence

The other major provision Cornyn identified as holding up the deal is how to define what a “boyfriend” is for the purpose of domestic violence. Currently, federal law bars anyone convicted of a domestic violence misdemeanor from owning or possessing firearms. However, the prohibition only extends to somebody who commits violence against someone they are married to, have a child with, live with, or are related to.

“The other issue has to do with the way that nontraditional relationships are handled in terms of domestic violence and misdemeanors,” Cornyn told Raju. “We’ve got to come up with a good definition of what that actually means.”

There is some difficulty in defining a romantic partner in federal law. Some Democrats apparently want to extend this to situations where people who dated at one point and then got into an altercation years after that point. Republicans are uncomfortable with that.

New Background Check Process for 18-20-Year-Olds With Juvenile Records and a De Facto Waiting Period

Surprisingly, Cornyn didn’t identify the details of checking juvenile records as one of the significant sticking points. That’s interesting since it is likely the most consequential change to federal gun laws in the entire package.

If the text of the provision matches a recent report in The Trace, the Senators are going to create an entirely new background check process for 18-to-20-year-olds that includes a de facto waiting period. That would represent a remarkable departure from how the National Instant Criminal Background Check System (NICS) has been designed to work since its inception back in 1993. Namely, that it would no longer be designed with instant checks in mind.

As the name implies, a NICS check is usually instantaneous. It does already have a process by which a check can be delayed for up to three days for the FBI to conduct a more thorough examination of a buyer’s criminal or mental health records. However, that only happens in the rare number of cases where the FBI identifies a potential disqualifying record, such as pending charges, but isn’t able to immediately obtain details on that record.

In contrast, the Senate deal seems to apply this delayed status to all buyers under the age of 21 in order to provide time for the FBI to locate potential juvenile criminal or mental health records.

That could prove controversial for a number of reasons. First and foremost, creating what is effectively a federal waiting period is likely to garner heated opposition from gun-rights groups, even if it is limited to younger adults. Many will see it as a slippery slope.

Then there’s the question of what juvenile records should be included as disqualifying and how those records can even be checked by the FBI. Lawmakers across the aisle have already started raising those concerns.

“The access to juvenile records will be a difficult piece of work because states have different laws with regards to that eliminating juvenile records,” Senator Mitt Romney (R., Utah), who has signed on to the framework, told NBC News on Monday. “And so how to deal with those differences will be a draft person’s nemesis.”

Prominent House Democrat Alexandria Ocasio-Cortez said she is particularly concerned about “the juvenile criminalization, the expansion of background checks into juvenile records.”

“I want to explore the implications of that and how specifically it’s designed and tailored,” she told The Independent’s Eric Michael Garcia on Monday. “After Columbine, we hired thousands of police officers into schools, and while it didn’t prevent many of the mass shootings that we’ve seen now, it has increased the criminalization of teens in communities like mine.”

Then there’s the issue that the new background check procedure appears to end once a buyer turns 21. Perhaps the text will provide further clarity, but it’s unclear why this new background check procedure is needed, and selected juvenile criminal records can’t simply be added to the current NICS process.

Deal Remains Likely

While all of these hangups could derail the deal, none of them are guaranteed to do so. The fact a deal had ten Republican votes right out of the gate gives it a lot of potential. That Minority Leader Mitch McConnell (R., Ky.) has expressed support for the deal, and Majority Leader Chuck Schumer (D., N.Y.) has committed to a vote as soon as possible, adds to the possibility. And Cornyn’s public doubt casting may simply be a negotiating tactic.

Shortly after Cornyn told CBS that he felt frustrated by talks on Thursday, Senator Kyrsten Sinema (D., Ariz.) interjected to say, “we’re optimistic!”

“Senator Sinema says I’m optimistic,” Cornyn replied.