A fast-rising number of people, including families, are approaching the U.S.-Mexico border. Many seek asylum. Now, President Biden wants Mexico to crack down on migrants, but Mexico is reaching its limits to do so.Read more:When President Barack Obama faced a steep rise in people migrating toward the southern U.S. border in 2014, he pressured Mexico to curb migration at its southern border with Guatemala. President Donald Trump did the same years later.Now, Mexico is once again facing pressure, this time from the Biden administration, to stop the number of people migrating north. But Mexico is reaching its limits as thousands of people cross into the country from throughout Latin America and other parts of the world. The Post’s Mary Beth Sheridan traveled to a migrant shelter in the central Mexican city of San Luis Potosí, where mattresses line a basketball court as the facility exceeds capacity.