All but one of about 50 undocumented Mexican migrants at a meeting Saturday indicated they would rather risk detention and long court battles in the U.S. than return to Mexico voluntarily.

The majority of migrants at the meeting in Phoenix, which included Mexican officials, signaled in a show of hands that they were ready to fight deportation in U.S. courts.

“Even if that means detention for weeks?” asked former foreign minister Jorge Castaneda.

“Even if it takes months,” shouted one woman. “Even if it takes years,” another yelled. “We are here to fight.”

Mr. Castaneda and others want Mexico’s government to endorse a tough and perhaps risky strategy to battle an expected increase in deportations of their undocumented compatriots in the U.S. by underwriting the migrants’ legal struggle in the U.S. court system. By overwhelming already heavily burdened immigration courts, Mr. Castaneda hopes the legal system would break down, bringing deportations to a halt.

Mexico’s government hasn’t endorsed the strategy, but President Enrique Peña Nieto recently budgeted about $50 million to the country’s 50 consulates to help pay the costs of defending migrants who are in the U.S. illegally and facing deportation.

Some are worried that President Donald Trump has decided to expand the type of undocumented migrants who are at risk of being deported, from the violent or dangerous people that the Obama administration targeted to migrants who have had minor brushes with law enforcement.

Mr. Trump on Sunday called it a “crackdown on illegal criminals,” adding in an early morning tweet that “Gang members, drug dealers & others are being removed!”

The Phoenix meeting took place two days after the deportation of a Guadalupe García, a 36-year-old Mexican who lived in the U.S. for 22 years and has two U.S.-born children. Ms. García’s removal stoked panic and protests in immigrant communities.

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