Then Lopez Obrador won the July 1 election by a landslide and his National Regeneration Movement party swept congressional and state elections. Suddenly AMLO, as he’s known from his initials, was Trump’s new best friend.

Following the election, Trump called Lopez Obrador, later telling reporters, “I think the relationship will be a very good one.” Days later, Trump sent down a delegation to meet with Lopez Obrador that included the secretaries of state, homeland security, and Treasury, and his son-in-law Jared Kushner. He later called the Mexican president-elect “a terrific person.”

What explains the sudden affinity for the Mexican progressive who dubbed Trump’s border politics a “hate campaign” and wrote an in-your-face book called “Listen Up, Trump” in defense of Mexican migrants in the U.S.?

Dozens of post-election articles have claimed that the two leaders’ populism makes them kindred spirits—albeit on opposite ends of the ideological spectrum. The comparison, usually illustrated by photos of Trump and Lopez Obrador sporting the same bulldog set of the jaw, panders to vacuous stereotypes and contains no intelligent political analysis.

There are, however, identifiable reasons for the current rapport. One stems from Trump’s ego: He respects Lopez Obrador’s electoral victory.

Trump warmed to Lopez Obrador because the president-elect’s remarkably successful campaign makes him a winner—and Trump identifies with winners (especially if they’re male). In a compliment that the U.S. president would usually reserve for himself, Trump wrote to his soon-to-be counterpart, “We both achieved electoral success by providing a clear vision for making our countries stronger and better.” In that vein, he has reportedly referred to Lopez Obrador as “Juan Trump.”

Trump and Lopez Obrador’s strong early relationship is also politically expedient for both. First, both want the North American Free Trade Agreement (NAFTA) off their political plates by the end of the year. They see the renegotiation process as a political liability that is causing unwelcome jitters in financial markets. Lopez Obrador wrote to Trump, “Prolonging the uncertainty could slow down investments in the medium- and long-term.” Lopez Obrador wants to leave the credit or the blame to the outgoing Mexican administration. Trump, for his part, wants to fulfill his campaign promise to fix or ditch NAFTA by the midterms.

Essentially, both want to conclude negotiations and claim they won. A compromise would probably look something like U.S. Treasury Secretary Steven Mnuchin’s “skinny NAFTA”—technical changes that don’t require congressional approval, and a non-binding agreement on raising wages in Mexico and prioritizing job creation in their respective countries.

The Mexicans will still have to face down Trump’s threats to reduce NAFTA to separate binational agreements with Mexico and Canada or to pull out altogether—a threat he repeated in his letter to Lopez Obrador: “I believe a successful renegotiation of [NAFTA] will lead to even more jobs and higher wages for hard-working American and Mexican workers—but only if it can go quickly, because otherwise I must go a much different route.”

Second, the two leaders agree on stemming immigration to the U.S., though for different reasons. Trump wants to keep immigrants out of the U.S. from a nativist stance that focuses on increased policing, barriers, and detention. To show progress, he needs Mexico to intensify efforts to “filter” migrants arriving through its southern border—a job Lopez Obrador does not relish.

The Mexican president-elect would rather work to create an economic system in which migration is optional, emphasizing job creation and educational opportunities in Mexico and Central America. He proposes a regional development plan focused on areas that expel migrants because of poverty and violence.

Third, during Mexico’s lame duck period and the run-up to the U.S. midterms, neither leader wants to rock the boat. Both need stable financial markets and an optimistic outlook for their parties to succeed.

The current coziness between Lopez Obrador and Trump, though, can’t last forever. Trump plays to an anti-immigrant, anti-Mexico base, and the Mexican population will never trust Trump or a Mexican president who appeases him. Clashes are inevitable between the state-primed economic revival and redistribution path Lopez Obrador has laid out and Trump’s America First strategy, motored by xenophobia and an expanding military-industrial complex.

If the aim of diplomacy is to provide stability and well-being to the people—as it should be—the basis of understanding will eventually have to include points on which the two leaders agree to disagree. Defining distance is as important as defining cooperation.

The odd couple’s honeymoon may be the prelude to a difficult marriage. Divorce isn’t an option, but separate bedrooms might not be a bad idea.

Laura Carlsen is the director of the Americas Program at the Center for International Policy.