The pro-NAFTA forces in Washington are escalating efforts to protect the agreement from President Donald Trump, including entertaining the idea of shielding it via some legislative mechanism.

The U.S. Chamber of Commerce announced it will hold weekly events to rally support for the deal, as the country's largest business lobby held an initial such gathering Tuesday at its headquarters across the street from the White House.

Speakers at the event were senators from the president's Republican party. They urged trade supporters to raise their voices to help sway an internal debate within the White House, as Trump considers whether to start the NAFTA cancellation process as a hardball negotiating ploy.

One senator from Kansas dismissed that as a "Humpty Dumpty" strategy — break NAFTA first, attempt to fix it later. Pat Roberts called it an unnecessarily risky move and said he has personally confronted the president three times over his approach to trade, including at a closed-door caucus meeting last week.

He said the president told Republican lawmakers not to get excited over his negotiating ploy, to which Roberts replied: "I am excited."

Roberts said it's imperative that people who believe in trade speak out now to counter the anti-trade impulses in Trump's Washington, echoing a message also delivered at Tuesday's event by his colleague Sen. Ted Cruz.

"Saddle up. Everybody saddle up. We have to ride. Ride with me," Roberts said in a speech.

"We are fighting a pervasive view that our economy has not benefited from NAFTA. That is simply not right. We are coming to a crossroads... These issues affect real jobs, real lives and real people."

Both senators described how their states have benefited from NAFTA. A new document produced by the Congressional Research Service on state-level trade data says Kansas exports about US$750 million in grain products to Mexico, and another $10 million to Canada.

Farming groups have spoken out too, warning that the mere threat to cancel NAFTA could send foreign customers scrambling to find new non-U.S. suppliers.

Roberts briefly addressed the emerging debate about what power Congress might have to block a presidential NAFTA pullout. Trade lawyers say it's unclear whether the president can act unilaterally, and some suggest such a move could wind up at the Supreme Court.

That's because the U.S. Constitution offers contradictory instructions: Its Article One gives Congress power over international trade, and Article Two gives the president power over foreign affairs.

Some analysts like former U.S. trade czar Robert Zoellick have urged Congress to flex its muscles by taking legislative steps to wrest some control away from the White House. Ideas being floated around Washington, for example, include attaching pro-NAFTA clauses to a bill, or passing a bill that would insist on a thorough study of the consequences before any U.S. pullout.

Asked whether his colleagues are discussing such steps, Roberts said it's a possibility: "That might be an option. Right now I think it would be a little early to be doing that... I think we can make our case before the administration," so it doesn't get there.

Cruz said his GOP colleagues are almost universally pro-trade.

"The Republican conference and Senate is virtually united," he told the business crowd. "I want to encourage everyone in this room: Let your voice be heard. Because the administration is being pulled in two different directions."

The U.S. Chamber of Commerce has sounded the alarm over what it sees as potentially fatal moves to undermine the agreement by the Trump administration amid negotiations to upgrade the deal.

Those moves include demands by the Trump administration for a five-year termination clause allowing easy cancellation of the agreement; tougher Buy American rules; auto-parts requirements the industry calls impossible to meet; and a gutting of the dispute mechanisms that enforce NAFTA.

"For many in the business and agriculture community, the outlook has shifted over the past month. There's growing concern about the direction of the negotiations," said John Murphy, the chamber's vice-president.

"A number of the proposals that the United States has put on the table have little or no support from the U.S. business and agriculture community. It isn't clear who they're intended to benefit.... (They) will only add costs for business, add to uncertainty, depress investment...

"But I think many in Congress are catching up to those concerns. They're increasingly hearing from their constituents. Threats to withdraw from the agreement are catching attention."

More than 80 agriculture groups wrote to the administration last week urging Trump not to use NAFTA's pullout clause as a negotiating tool. That clause, Article 2205, allows a country to provide six months' notice of its intention to withdraw.

"Withdrawal is looked upon as a potential catastrophe,'' Murphy said. ''So I do think members of Congress are rapidly coming to grips with those concerns, as they're hearing them from their constituents."

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