President Donald Trump is threatening to start a trade war with Mexico, but Mexico’s populist President Andrés López Obrador isn’t having it.

Trump warned Thursday evening, over Twitter, that he would soon start taxing imported goods from Mexico if the government doesn’t do more to stop the flow of migrants from Central America who are seeking asylum at the US border.

López Obrador responded within a few hours with a scathing letter that he posted on Twitter. He invoked Abraham Lincoln and Franklin D. Roosevelt, pointing out that those US presidents respected Mexico’s sovereignty — a veiled warning for Trump to back off.

“President Trump: You can’t solve social problems with taxes or coercive measures,” López Obrador wrote. He added that he prefers dialogue, not confrontation, which suggests that he doesn’t want to retaliate by taxing US goods.

López Obrador, known to his supporters affectionately as AMLO, also slammed Trump’s “America First” rhetoric and condemned his administration’s cruelty toward immigrants:

How does one transform, overnight, the country of fellowship with immigrants from around the world into a ghetto, a closed-off space that stigmatizes, mistreats, chases, expels and cancels legal rights to those who are seeking —with effort and hard work— to live free of misery? The Statue of Liberty isn’t an empty symbol.

The Trump administration has grown increasingly frustrated with the growing number of Central American immigrants passing through Mexico to request asylum in the US. Border crossings in May jumped to the highest level in more than 12 years, according to the Department of Homeland Security, and the large number of families with children are overwhelming the Customs and Border Protection officers.

But slapping tariffs on goods from Mexico is a bizarre way to deal with the problem. It could sabotage Trump’s new trade deal with Canada and Mexico to replace NAFTA, and would likely end up hurting American companies and consumers more than anyone in Mexico.

Still, the threat seemed intended to scare López Obrador into taking more extreme action on immigration, such as closing off Mexico’s border with Guatemala and arresting people who help migrants get to the US.

López Obrador, unlike past Mexican presidents, isn’t inclined to bow to US pressure and has taken a less combative approach toward migrants than some of his predecessors. In his letter, he said his government is already doing a lot to prevent illegal migration through Mexico, and urged Trump to focus on the root cause of the problem: violence and poverty in Central America.

Here’s his full letter to Trump, translated from Spanish:

President Donald Trump:

I’ve learned about your latest position regarding Mexico. First of all, I want to express that I do not want a confrontation. When facing a conflict in our relationship, no matter how serious, the cities and nations we represent deserve that we turn to dialogue and act with caution and responsibility.

Mexico’s best president, Benito Juárez, maintained an excellent relationship with his Republican counterpart, Abraham Lincoln. Later on, during the oil expropriation (when Mexico kicked out foreign oil companies), Democratic President Franklin D. Roosevelt understood the profound reasons that led patriot President Lázaro Cárdenas to act in favor of our sovereignty. Indeed, President Roosevelt was a titan of liberty. Before anyone else, he proclaimed the four fundamental human rights: the right to speak freely, to practice religion freely, to live free of fear, and to live free of misery.

That’s the thinking behind our politics when it comes to the migration issue. Human beings don’t abandon their hometowns because they want to, but because they need to. That’s why, when I first took office, I proposed to partner in helping develop Central American countries by making productive investments that will create jobs and address the root cause of this terrible issue.

You must also know that we are complying with our responsibility to prevent, to the extent possible and without violating human rights, passage through our country. It’s worth reminding you that, before long, Mexicans will no longer need to go to the United States, and that migration will be optional, not forced. That’s because we are fighting corruption, Mexico’s main problem, like never before! And that’s how our country will become a great power with a social dimension. Our fellow citizens will be able to work and be happy where they were born, where their families, traditions and cultures are.

President Trump: You can’t solve social problems with taxes or coercive measures. How does one transform, overnight, the country of fellowship with immigrants from around the world into a ghetto, a closed-off space that stigmatizes, mistreats, chases, expels and cancels legal rights to those who are seeking —with effort and hard work— to live free of misery? The Statue of Liberty isn’t an empty symbol.

With all due respect, while you have the sovereign right to say it, the slogan “America First” is a fallacy, because until the end of times, and above national borders, universal justice and brotherhood will prevail.

More specifically, my fellow president: I propose that we deepen our dialogue to find alternative solutions to the root cause of the migration problem, and please, remember that I don’t lack courage, that I am not a coward or timid, but that I act based on principles: I believe that politics, among other things, was invented to avoid confrontation and war. I do not believe in the Talion Law, in a “tooth for a tooth” or an “eye for an eye,” because, if we go there, we’d all end up toothless and blind in one eye. I believe that people of the state, and even more so, as people of the nation, we are obligated to find peaceful solutions to our disputes and to always practice the beautiful ideal of non-violence.

Lastly, I propose that you instruct your staff, if it’s not an inconvenience, to meet with representatives of our government, led by Mexico’s secretary of foreign relations, who are heading to Washington tomorrow so we can find a solution that benefits both our nations.

Nothing by force, everything with reason and by the Law!

Your friend,

Andrés Manuel López Obrador

President of Mexico