Senate Republicans have strategically revved up their attempt to convince President Trump to not withdraw from NAFTA. Some senators and aides say he may not have understood how popular it was with the caucus until recently, and are encouraging him to focus instead on improving it.

Why this matters: This is Congress’s clearest shot at saving the trade agreement. If Trump decides to withdraw, Congress probably couldn’t stop him, and both the legal and economic consequences are extremely unclear.

Where it stands: Senate Republicans stepped up their attempts to educate Trump on the benefits of NAFTA in the late fall, going to the White House and speaking to administration members to make their case. Almost every senator I spoke with say they think it's working, but some are still more nervous than others.

Several noted that in his remarks to the American Farm Bureau on Monday night, the president didn't threaten to withdraw from the agreement, saying instead he wants the best trade deals possible.

"I think if you look at his statement very carefully, he did not mention termination ... I think he’s made some real progress," said Sen. Pat Roberts, chairman of the Senate Agriculture Committee and a leading pro-NAFTA voice in the Senate.

Some senators say they think Trump only began to understand their position once they increased their outreach to him. “That’s why we’re taking the time to share our message with him. But I think it’s made a very positive impact," said Sen. Joni Ernst.

Trump has been bringing it up with some senators to get their opinion lately, not the other way around. Sen. Bob Corker said that on Monday, he visited with the president to discuss Iran, but Trump brought up NAFTA.

If he withdraws, it's not clear what Congress could do. This is partially why lawmakers are going on the offense right now.

Lawyers are scrambling to figure out how this all would work. The first step would be giving a six-month notice of withdrawal, which is non-binding but still something senators generally don't want.

While it seems likely that the president has the authority to withdraw from NAFTA without congressional approval, there would surely be litigation on the subject.

“I know any changes that are made have to be approved by Congress, but I don’t know what the law says about getting out of it, whether we have a voice in that or whether the president can do that," said Sen. Chuck Grassley.

It's also unclear what the economic consequences would be. Several senators told me they've talked to Trump about how ingrained NAFTA is in their states' economies, noting that ending the agreement could cause job losses and recessions in certain sectors.

Their message to Trump: Find a way to get a win without withdrawing, and take it.

Senators and aides made it clear they think NAFTA can be updated.

"This is a situation where we have to present the reasons why we believe NAFTA makes our country stronger. And he believes he can make NAFTA stronger. I think those are two common sense goals that aren’t mutually exclusive," Sen. Cory Gardner told me, who has been active in the effort to court Trump over the past couple months.

"Our point is, it’d be a paradox and an enormous irony if during a time we hope to see this economic growth because of the tax bill, that we get into a farm recession because we’re not selling our products," Roberts said.

Another argument that's been made is withdrawal could hurt the stock market, which is doing extremely well right now — as Trump likes to tweet about.

The bottom line: Senators seem optimistic that the president is listening to them and will decide to focus on improving the trade agreement, not withdrawing from it. But Trump is known for changing his mind at the drop of a hat, so no one should feel in the clear yet.

"I’m very concerned and don’t have a sense of what the administration’s going to do," said Sen. Jerry Moran. "In other words, I would not be surprised by a withdrawal, and I think the consequences of that are significantly damaging.”