Washington (CNN) The issue of gun control always comes up in Congress after a mass shooting in the US -- but there haven't been any major gun reform laws in more than two decades.

President Donald Trump has suggested he's open to new gun control laws, and started a discussion about what lawmakers can do to address mass shootings in the US after he announced his support to ban bump stocks

Congress, which is back in session this week, could address the debate over gun laws.

Here's a look at five proposals they could consider:

1. Legislation to outlaw bump stocks (backing up the ATF) -- has bipartisan support

Trump said Tuesday that he directed Attorney General Jeff Sessions to propose changes that would ban bump fire stocks , which can be attached to a semi-automatic weapon to make it easier to fire rounds more quickly, similar to that of an automatic weapon.

He said he wanted the Department of Justice to "propose regulations that ban all devices that turn legal weapons into machine guns."

But Democrats argue he will need to endorse legislative action if he really wants to see a change.

In a statement after Trump's announcement, Senate Minority Leader Chuck Schumer referred to California Democratic Sen. Dianne Feinstein's bump stock ban proposal last year.

"There are serious problems with the President's approach. First, his own ATF agency has warned that it does not have the authority to ban bump stocks. The only way to close this loophole permanently is legislation," Senate Minority Leader Chuck Schumer said in his statement. "He should call on Congress to pass Senator Feinstein's bill to ban bump stocks, rather than just draft memos. On far too many issues, this administration has been all talk and little action -- we can't afford that approach when it comes to curbing gun violence."

Feinstein, a California Democrat, who submitted a bill last year in the Senate that would ban bump stocks -- welcomed Trump's support for a ban, but cautioned that new agency rules could fail because of the Bureau of Alcohol, Tobacco, Firearms and Explosives' past stance on the devices.

"If ATF tries to ban these devices after admitting repeatedly that it lacks the authority to do so, that process could be tied up in court for years, and that would mean bump stocks would continue to be sold," Feinstein said.

It's likely this issue will be addressed next week, considering Trump's request to ban the gun accessory.

There is a bipartisan bill in the House to ban bump stocks, but House Speaker Paul Ryan has deferred to the ATF to address the issue rather than schedule a vote on the measure. "We think the regulatory fix is the smartest, quickest fix," he said during his weekly news conference at Capitol Hill, after the mass shooting in Las Vegas.

It's unclear whether Trump's support for the proposal will add some pressure for a vote or if leaders, again pointing to the President's action already on the issue, will simply wait on action by the executive branch.

2. Background checks -- has bipartisan support

After the shooting in Parkland, Florida, the White House said Trump "is supportive of efforts to improve the federal background check system" for gun purchases.

Trump spoke with Sen. John Cornyn, a Texas Republican and the second ranking GOP member in the chamber, about a bill he introduced with Sen. Chris Murphy, a Connecticut Democrat, that aims to strengthen how state and federal governments report offenses that could prohibit people from buying a gun.

In simple terms, the bill would hold federal and state agencies accountable if they fail to upload criminal history records to the background check system.

The bill wouldn't strengthen background checks, but instead require the National Criminal Instant Background Check system stay updated.

This narrow proposal that now has the endorsement of the President could have some momentum now, but Democrats are already insisting that it's just a first step and want broader action to close what they argue are loopholes on background checks on the sale of guns online and at gun shows.

3. Raising gun age -- has bipartisan support

Currently, US law allows someone who is 18 and older to be able to purchase a rifle or shotgun.

Republican Sen. Marco Rubio of Florida suggested during a CNN town hall last week that there's possibly enough votes in the Senate to change the legal age to purchase a rifle from 18 to 21.

A kid too young buy a handgun should be too young to buy an #AR15. Working with @SenFeinstein on a bipartisan bill that will raise the minimum purchase age for non-military buyers from 18 to 21 - the same age you currently have to be to purchase a handgun. — Jeff Flake (@JeffFlake) February 21, 2018

Sen. Jeff Flake of Arizona, also a Republican, said Wednesday he'd back such a proposal, lending bipartisan support to legislation that was introduced earlier this month by Feinstein in the wake of the mass shooting at a high school in Parkland, Florida. And GOP Sen. Pat Roberts is also voicing support for restricting access to semiautomatic rifles for those under the age of 21.

"Certainly nobody under 21 should have an AR-15," the Kansas Republican said when speaking to reporters at the Kansas Statehouse, Roberts press aide Sarah Little confirmed to CNN Thursday.

The idea has emerged as potential compromise among GOP and Democratic lawmakers -- who are sharply divided and therefore gridlocked on gun control issues -- as they search for a response to shooting in Parkland.

Although Trump backed this proposal, the NRA quickly came out against it and it faces an uphill battle in Congress. Cornyn told CNN on Friday he did not think the effort would save lives and wasn't sure the measure would be able to pass the chamber.

4. Gun magazine size restriction -- unlikely to have bipartisan support

At CNN's gun town hall on Wednesday night, Rubio said while he had not in the past supported looking at magazine clip size, he was now "reconsidering that position."

"I'll tell you why," Rubio said on the issue at the town hall. "Because while it may not prevent an attack, it may save lives in an attack."

Immediately after, Democratic Sen. Bob Menendez of New Jersey tweeted at Rubio, sharing the bill he introduced after the Las Vegas shooting that, if implemented, would ban the importation, sale, manufacture, transfer or possession of gun magazines that hold more than ten rounds of ammunition.

Menendez wrote, "Thank you for reconsidering your position on large capacity magazines at the CNN Town Hall - I've got a bill waiting for you to co-sponsor."

Sen. @marcorubio, thank you for reconsidering your position on large capacity magazines at the CNN Town Hall - I've got a bill waiting for you to co-sponsor —> https://t.co/gBB3DBrJYB — Senator Bob Menendez (@SenatorMenendez) February 22, 2018

Although Rubio's shift was noteworthy there is no indication that there are large numbers of Republicans that would back this, but gun control advocates will again push for this to be part of the debate.

5. Banning AR-15 style weapons -- very unlikely to have bipartisan support

While some gun control advocates have called for a ban on AR-15-style guns, similar to one the US had in place until it expired in 2004, it's unlikely that Congress will revisit the issue any time soon -- but a discussion on the issue from Parkland shooting survivors has come up.

The Colt AR-15, the style of gun on which the Parkland shooting weapon was based, was among those outlawed for 10 years under a 1994 law banning its sell and production, but is now legal again.

At the CNN town hall Wednesday, Rubio was asked by a father, whose daughter was killed in Parkland, about banning semi-automatic rifles such as the one used in the Parkland shooting, and he argued it wouldn't have prevented the school shooting.

The Florida House considered and then rejected a ban on many semiautomatic guns and large capacity magazines as dozens of survivors of last week's school shooting headed to the state Capitol to turn their grief into political action.