(CNN) As Congress returns to Washington this week, a sweeping and polarizing debate on guns is waiting for them, and lawmakers must decide if it's one they're willing to tackle just months ahead of the midterm elections.

Control of the Senate is up for grabs , though Democrats face a steep climb to regain the majority as they have 10 seats in states President Donald Trump won that they must defend. The thin margin for control in the chamber is a powerful force pressuring both sides in the coming weeks as they decide how far they're willing to go -- if anywhere -- on addressing gun violence and mass shootings.

Pushed by Trump to do something, Republicans could be forced to choose between the President's wishes and some of the National Rifle Association's red lines.

Trump spent last week in listening sessions with survivors of the Parkland, Florida, shooting and with law enforcement officials. But Capitol Hill aides say a key factor in whether they push to change gun laws is whether Trump -- who is prone to changing his mind on policy priorities and careening abruptly from one topic to another -- will remain focused this week on the issue.

Democrats in those Trump states -- as well as some in leadership -- must also consider the political ramifications of a gun debate, leaving open the question of whether lawmakers will engage this week.

"Until the majority leader speaks, I don't think anybody should assume there is going to be any debate," Sen. Chris Murphy, a Democratic senator from Connecticut told CNN on Friday, referencing the role Senate Majority Leader Mitch McConnell of Kentucky would have to play for the chamber to act on guns.

Background checks gets new push

While Trump has encouraged lawmakers to look at background checks and raising the legal age to purchase rifles from 18 to 21, it is Senate and House leaders who will make the ultimate call on what comes to the floor of their respective chambers. Republicans and Democrats will each huddle for the respective party lunches on Tuesday, which may be the earliest indication of whether Congress plans to act on even narrow proposals.

"I'm not sure if he knows what that means," Murphy said. "That generally means universal background checks applying to all commercial sales, but he has not backtracked on that tweet since he made it."

Murphy has partnered with Senate Majority Whip John Cornyn, a Texas Republican, on legislation that aims to shore up compliance in reporting to the National Instant Criminal Background Check System. According to Cornyn, there is a bipartisan conversation underway about whether the Senate could get agreement to vote on the so-called Fix NICS bill as soon as Monday, which could limit debate and hold off tough amendments on both sides of the aisle, but that would require every single member of the Senate to agree to bring it up.

For now, it appears that any gun debate would likely include just modest changes to gun laws, like the proposal to strengthen the National Instant Criminal Background Check System by incentivizing states and agencies to more readily include valuable records into the system.

The House already passed that bill in December although it was attached to another proposal that would allow individuals with concealed carry permits to transport their guns across state lines. The concealed carry bill would likely be dead on arrival in the Senate.

Cornyn signals opposition to changing gun age limit

While some Republican senators, like Florida's Marco Rubio and Kansas' Pat Roberts, have signaled a willingness to raise the age at which individuals can purchase rifles from 18 to 21, other key leaders have broken with Trump.

"I think what we want to focus on is things that will actually save lives," Cornyn, the GOP vote counter, told CNN on Friday when asked if he supported raising the age limit. "That's why I think the focus should be on the Fix NICS bill, which is the only bipartisan piece of legislation that can be signed into law."

"There are a lot of other ideas out there that people are proposing and that I don't think will actually change any outcomes," he added.

Cornyn, who was in the Capitol on Friday to preside over a brief pro forma session, said he thought an age restriction would be problematic if an 18-year-old Marine or police officer were told he or she could not buy a gun.

"I can see that it would be difficult to enforce. I'm not sure why we would go to those lengths when I don't think that gets to the root of the problem," he said.

What's different this time

Senators have been through this debate before. In 2012, after the shooting at Sandy Hook Elementary School in Newtown, Connecticut, which left 26 dead, including 20 children, the Senate tried and failed to ban assault weapons , to limit the size of high-capacity magazines and require more background checks. Lawmakers failed even with a Democratic president and Democratic Senate in part because of opposition from red state Democrats.

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"There are always political ramifications with these votes," said Mike Saccone, a former aide to former Democratic Sen. Mark Udall of Colorado. "I don't think the politics around the issue have gotten any less difficult."

A calculation will still have to be made about whether Democrats want to enter into an unpredictable gun debate that could end with little more than a narrow bill to fix the criminal background check system.

"It's better to get that bill passed than not to get it passed," one Democratic Senate aide told CNN. "We should do this either way."

Sen. Amy Klobuchar, one of two Democratic senators from Minnesota seeking to keep their jobs this year in a state Hillary Clinton won by fewer than two percentage points, says she would like to see the Senate vote on a ban of assault-style weapons. She told NBC over the weekend that residents in her state "understand as law-abiding gun owners that we need to make change."

"And I think these students are going to lead the way and we're going to finally see some action," Klobuchar said Sunday on NBC's "Meet The Press." "And when I had those Sandy Hook parents in my office, and they told their stories, and you think about the courage they had to come forward on a simple background check bill, and then the Congress didn't have the courage to pass it, I don't think you're going to see that happen again."