MEXICO CITY, Mexico (AP) — President Donald Trump is sending his top diplomat and homeland security chief to Mexico on a fence-mending mission made all the more challenging by the actual fence he wants to build on the southern border.

Ties between the countries have plunged since Trump took office a month ago, punctuated by Trump’s insistence that Mexico pay for a border wall and other demands on illegal immigration and trade. And in Mexico, US Secretary of State Rex Tillerson and Homeland Security Secretary John Kelly will face a government anxiously rethinking its relationship with its bigger, richer and more powerful neighbour.

Tillerson was arriving Wednesday evening in Mexico City. Kelly, whose agency is responsible for implementing Trump’s immigration crackdown, was to arrive separately after visiting Guatemala. They plan to meet Mexican President Enrique Pena Nieto and other top officials.

The visit is part of a Trump administration trend: top Cabinet and other officials seeking to calm nervous nations that their US partnerships are secure in the new era of “America First.” Vice President Mike Pence and Defence Secretary Jim Mattis have previously filled the role, facing foreign leaders who’ve struggled to reconcile the rhetoric of reassurance with the declarations of disruption from Trump and some of his senior envoys.

Tillerson, the former Exxon Mobil CEO, and Kelly, a retired Marine general, have taken a more diplomatic tack toward Mexico than Trump, even as they both assume key roles in executing policy that has stirred widespread resentment in America’s southern neighbour.

On Tuesday, the US changed immigration enforcement policies that could subject millions of people living in the US illegally — including many Mexicans— to deportation. Whereas President Barack Obama focused on deporting immigrants convicted of serious crimes, new memos signed by Kelly prioritise deportation for anyone convicted of a crime or charged with any offence. That includes crossing the border illegally.

The memos also call for sending some people who enter the US illegally back to Mexico, even if they’re from Central America or elsewhere and only used Mexico as a transit point. Detention centre capacity will expand; planning for Trump’s much touted wall will begin.

All these actions are prompting consternation in Mexico. But the Trump administration believes the US can pursue a productive relationship with Mexico nonetheless, building on longstanding economic and other cooperation.

Trump was in office barely a week when Pena Nieto cancelled a planned visit to the US. The American leader had suggested their meeting would be ill-advised if Mexico wasn’t willing to pay for the wall, expected to cost billions of dollars. Mexico remained unwilling. A meeting between the two presidents hasn’t been rescheduled.

Anti-Trump protests have erupted in Mexico. Earlier this month, some 20,000 people marched through Mexico’s capital demanding respect from the US While Pena Nieto has struggled with plummeting approval ratings, his opposition to Trump has rallied many Mexicans around him.

Beyond the wall, Tillerson is likely to face questions about Trump’s pledge to renegotiate the North American Free Trade Agreement.

Eighty per cent of Mexico’s exports are to the US. The Trump administration also has floated the idea of a border tax on Mexican products.

A trio of Democratic senators visited Mexico in advance of Tillerson and Kelly’s trip. Putting the blame on Trump, Senator Ben Cardin of Maryland, the Senate Foreign Relations Committee’s top Democrat, said he was confident the relationship could withstand “140-character broadsides or unrealistic demands” — referring to the president’s frequent Twitter missives.