Mr. López Obrador and officials in his delegation to Washington say they are optimistic about reaching a deal with the Trump administration. The Mexican president suggested over the weekend that he was willing to “reinforce” the government’s migration-control strategies — as long as human rights were not violated.

But on Monday, Mexico’s ambassador to the United States, Martha Bárcena, said there was a limit to the Mexicans’ flexibility in the negotiations. “And the limit is Mexican dignity,” she said.

Mr. López Obrador has for months been pushing a strategy to address the migration crisis by attacking the root problems that are compelling people to leave their homelands.

Supporters of the approach hope the United States will become a major donor and participant. But Mr. Trump has instead moved to cut aid to the three Central American countries that send most of the migrants trying to cross the United States’ southwest border.

Last week, the Trump administration signed a two-year agreement to deploy up to 80 agents from the Department of Homeland Security to Guatemala to help train its law enforcement officials and conduct investigations aimed at stemming illegal migration.

But analysts wonder whether the American offer will extend much further.

“López Obrador is right that the only long-term solution for stopping out-migration from Central America is to invest in security and prosperity in the countries of origin,” Mr. Selee said. “But it’s unclear whether his government will put serious resources into this, and even less clear if the Trump administration will help.”