While the Mexican government clearly took issue with Trump's assertions about who would pay for the wall, it also said, "The Mexican government takes this opportunity to express its full solidarity with the people and government of the United States as a result of the damages caused by Hurricane Harvey in Texas, and expresses that it has offered to provide help and cooperation to the U.S. government in order to deal with the impact of this natural disaster—as good neighbors should always do in trying times."
Even as Trump attacked and criticized Mexico on Twitter, it still felt inclined to offer Texas and the U.S. its support amid a natural disaster, but it's not clear whether Trump will accept this assistance. 
In a statement emailed to The Washington Post Sunday night, the U.S. State Department said, "It is common during hurricanes and other significant weather events for the U.S. Government to be in close contact with our neighbors and partners in the region to share data and cooperate as needed and appropriate. If a need for assistance does arise, we will work with our partners, including Mexico, to determine the best way forward."
This isn't the first time Mexico has offered to help Americans in need. In 2005, the Mexican military provided aid in Louisiana and Mississippi following Hurricane Katrina. Over three weeks, it served 170,000 meals, helped distribute more than 184,000 tons of supplies and conducted more than 500 medical consultations, the Post reported. The assistance Mexico provided helped save lives. 
Former Mexican President Vicente Fox, who led the country during Katrina (and who's been an outspoken critic of Trump), recalled in a tweet how his country assisted the U.S. in 2005 and asked whether Trump would "let Mexicans help this time."

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